Optimize anonymous swapbacked large folio unmapping
Subsystems (6)
cover Optimize anonymous swapbacked large folio unmapping
Speed up unmapping of anonymous swapbacked large folios by clearing the ptes, and setting swap ptes, in one go.
The following benchmark (stolen from Barry) is used to measure the time taken to swapout 256M worth of memory backed by 64K large folios:
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>
#define SIZE_MB 256
#define SIZE_BYTES (SIZE_MB * 1024 * 1024)
int main() {
void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (addr == MAP_FAILED) {
perror("mmap failed");
return 1;
}
memset(addr, 0, SIZE_BYTES);
struct timespec start, end;
clock_gettime(CLOCK_MONOTONIC, &start);
if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) {
perror("madvise(MADV_PAGEOUT) failed");
munmap(addr, SIZE_BYTES);
return 1;
}
clock_gettime(CLOCK_MONOTONIC, &end);
long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 +
(end.tv_nsec - start.tv_nsec);
printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n",
duration_ns, duration_ns / 1e6);
munmap(addr, SIZE_BYTES);
return 0;}
Performance as measured on a Linux VM on Apple M3 (arm64):
Vanilla - Mean: 37401913 ns, std dev: 12%
Patched - Mean: 17420282 ns, std dev: 11%
resulting in more than 2x speedup.
No regression observed on 4K folios.
Performance as measured on bare metal x86:
Vanilla - mean: 54986286 ns, std dev: 1.5%
Patched - mean: 51930795 ns, std dev: 3%
I tried magnifying the difference on x86 by using 1M large folios, but can't spot an obvious improvement (looks like my system is too fast to benefit from batched atomic operations!), hinting that the benefit lies mainly in the reduction of ptep_get() calls and the reduction of TLB flushes during contpte-unfolding, on arm64.
No regression is observed on 4K folios on x86 too.
---
Applies on mm-new (3d18f3499c48). mm-selftests pass.
This breakout patchset is the final completion of
https://lore.kernel.org/all/[email protected]/
The extra addition is the generic set_softleaf_ptes() helper.
Dev Jain (8):
mm/swapfile: add batched version of folio_dup_swap mm/swapfile: add batched version of folio_put_swap mm/rmap: mm/rmap: Add batched version of folio_try_share_anon_rmap_pte mm/internal: rename swap offset helpers to softleaf offset mm/internal: add set_softleaf_ptes
mm/memory: use set_softleaf_ptes for uffd-wp markers
mm: move anon-exclusive batch helper to internal.h mm/rmap: batch unmap anonymous swap-backed large folios
include/linux/rmap.h | 51 +++++++++++++------- mm/internal.h | 79 +++++++++++++++++++++++++------ mm/memory.c | 20 +++----- mm/mprotect.c | 17 ------- mm/rmap.c | 109 +++++++++++++++++++++++++++++++------------ mm/shmem.c | 8 ++-- mm/swap.h | 35 ++++++++++++-- mm/swapfile.c | 31 ++++++------ 8 files changed, 235 insertions(+), 115 deletions(-)
Signature · 1 line
2.43.0
PATCH 1/8 mm/swapfile: add batched version of folio_dup_swap
Add folio_dup_swap_pages to handle a batch of consecutive pages. Note that folio_dup_swap already can handle a subset of this: nr_pages == 1 and nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages.
Currently we have a not-so-nice logic of passing in subpage == NULL if we mean to exercise the logic on the entire folio, and subpage != NULL if we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokes folio_dup_swap_pages() if it wants to operate on a range of pages in the folio (i.e nr_pages may be anything between 1 and folio_nr_pages()), and invokes folio_dup_swap() if it wants to operate on the entire folio.
--- mm/rmap.c | 2 +- mm/shmem.c | 2 +- mm/swap.h | 18 ++++++++++++++++-- mm/swapfile.c | 14 ++++++-------- 4 files changed, 24 insertions(+), 12 deletions(-)
mm/rmap.c +1 -1
@@ -2148,7 +2148,7 @@ static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,swp_entry_t entry =page_swap_entry (page);struct mm_struct *mm = vma->vm_mm; -if (folio_dup_swap (folio, page) <0 ) +if (folio_dup_swap_pages (folio, page,1 ) <0 )return false;/*
mm/shmem.c +1 -1
@@ -1698,7 +1698,7 @@ int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,spin_unlock (&shmem_swaplist_lock); } -folio_dup_swap (folio,NULL ); +folio_dup_swap (folio);shmem_delete_from_page_cache (folio,swp_to_radix_entry (folio->swap));BUG_ON (folio_mapped (folio));
mm/swap.h +16 -2
@@ -251,7 +251,8 @@ extern int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp);* folio_put_swap(): does the opposite thing of folio_dup_swap(). */ int folio_alloc_swap (struct folio *folio); -int folio_dup_swap (struct folio *folio,struct page *page); +int folio_dup_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages);void folio_put_swap (struct folio *folio,struct page *page);/* For internal use */
@@ -375,7 +376,8 @@ static inline int folio_alloc_swap(struct folio *folio)return -EINVAL ; } -static inline int folio_dup_swap (struct folio *folio,struct page *page) +static inline int folio_dup_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) {return -EINVAL ; }
@@ -470,6 +472,18 @@ static inline void __swap_cache_replace_folio(struct swap_cluster_info *ci, }#endif /* CONFIG_SWAP */ +/** +* folio_dup_swap() - Increase swap count of all swap entries of a folio. +* @folio: folio with swap entries bound. +* +* See folio_dup_swap_pages() for more information. +*/ +static inline int folio_dup_swap (struct folio *folio) +{ +return folio_dup_swap_pages (folio,folio_page (folio,0 ), +folio_nr_pages (folio)); +} +extern const struct swap_ops swap_bdev_ops; int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
mm/swapfile.c +6 -8
@@ -1785,9 +1785,10 @@ int folio_alloc_swap(struct folio *folio) }/** -* folio_dup_swap() - Increase swap count of swap entries of a folio. +* folio_dup_swap_pages() - Increase swap count of swap entries of a folio. * @folio: folio with swap entries bounded. -* @page: if not NULL, only increase the swap count of this page. +* @page: the first page in the folio to increase the swap count for. +* @nr_pages: the number of pages in the folio to increase the swap count for. * * Typically called when the folio is unmapped and have its swap entry to * take its place: Swap entries allocated to a folio has count == 0 and pinned
@@ -1801,18 +1802,15 @@ int folio_alloc_swap(struct folio *folio)* swap_put_entries_direct on its swap entry before this helper returns, or * the swap count may underflow. */ -int folio_dup_swap (struct folio *folio,struct page *page) +int folio_dup_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) {swp_entry_t entry = folio->swap; -unsigned long nr_pages =folio_nr_pages (folio);VM_WARN_ON_FOLIO (!folio_test_locked (folio), folio);VM_WARN_ON_FOLIO (!folio_test_swapcache (folio), folio); -if (page) { - entry.val +=folio_page_idx (folio, page); - nr_pages =1 ; - } + entry.val +=folio_page_idx (folio, page);return swap_dup_entries_cluster (swap_entry_to_info (entry),swp_offset (entry), nr_pages);
Signature · 1 line
2.43.0
Re: [PATCH 1/8] mm/swapfile: add batched version of folio_dup_swap
Quoted 13 lines · Dev Jain
Add
folio_dup_swap_pagesto handle a batch of consecutive pages. Note thatfolio_dup_swapalready can handle a subset of this:nr_pages== 1 andnr_pages==folio_nr_pages(folio). Generalize this to anynr_pages.Currently we have a not-so-nice logic of passing in subpage == NULL if we mean to exercise the logic on the entire folio, and subpage != NULL if we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokesfolio_dup_swap_pages()if it wants to operate on a range of pages in the folio (i.enr_pagesmay be anything between 1 andfolio_nr_pages()), and invokesfolio_dup_swap()if it wants to operate on the entire folio.
Quoted 2 lines
Signed-off-by Dev Jain <[email protected]>
Yep, also I like that the page == NULL case is no longer needed in shmem.c.
PATCH 2/8 mm/swapfile: add batched version of folio_put_swap
In reply to Dev JainAdd folio_put_swap_pages to handle a batch of consecutive pages. Note that folio_put_swap already can handle a subset of this: nr_pages == 1 and nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages.
Currently we have a not-so-nice logic of passing in subpage == NULL if we mean to exercise the logic on the entire folio, and subpage != NULL if we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokes folio_put_swap_pages() if it wants to operate on a range of pages in the folio (i.e nr_pages may be anything between 1 and folio_nr_pages()), and invokes folio_put_swap() if it wants to operate on the entire folio.
--- mm/memory.c | 6 +++--- mm/rmap.c | 4 ++-- mm/shmem.c | 6 +++--- mm/swap.h | 17 +++++++++++++++-- mm/swapfile.c | 17 ++++++++--------- 5 files changed, 31 insertions(+), 19 deletions(-)
mm/memory.c +3 -3
@@ -5198,7 +5198,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)if (unlikely (folio != swapcache)) {folio_add_new_anon_rmap (folio, vma, address,RMAP_EXCLUSIVE );folio_add_lru_vma (folio, vma); -folio_put_swap (swapcache,NULL ); +folio_put_swap (swapcache); }else if (!folio_test_anon (folio)) {/* * We currently only expect !anon folios that are fully
@@ -5207,12 +5207,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)VM_WARN_ON_ONCE_FOLIO (folio_nr_pages (folio) != nr_pages, folio);VM_WARN_ON_ONCE_FOLIO (folio_mapped (folio), folio);folio_add_new_anon_rmap (folio, vma, address, rmap_flags); -folio_put_swap (folio,NULL ); +folio_put_swap (folio); }else {VM_WARN_ON_ONCE (nr_pages !=1 && nr_pages !=folio_nr_pages (folio));folio_add_anon_rmap_ptes (folio, page, nr_pages, vma, address, rmap_flags); -folio_put_swap (folio, nr_pages ==1 ? page :NULL ); +folio_put_swap_pages (folio, page, nr_pages); } VM_BUG_ON(!folio_test_anon(folio) ||
mm/rmap.c +2 -2
@@ -2157,13 +2157,13 @@ static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,* so we'll not check/care. */ if (arch_unmap_one (mm, vma, address, pteval) <0 ) { -folio_put_swap (folio, page); +folio_put_swap_pages (folio, page,1 );return false; }/* See folio_try_share_anon_rmap(): clear PTE first. */ if (anon_exclusive &&folio_try_share_anon_rmap_pte (folio, page)) { -folio_put_swap (folio, page); +folio_put_swap_pages (folio, page,1 );return false; }
mm/shmem.c +3 -3
@@ -1719,7 +1719,7 @@ int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,/* Swap entry might be erased by racing shmem_free_swap() */ if (!error) {shmem_recalc_inode (inode,0 , -nr_pages); -folio_put_swap (folio,NULL ); +folio_put_swap (folio); }/*
@@ -2149,7 +2149,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index, nr_pages =folio_nr_pages (folio);folio_wait_writeback (folio); -folio_put_swap (folio,NULL ); +folio_put_swap (folio);swap_cache_del_folio (folio);/* * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks
@@ -2379,7 +2379,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,if (sgp ==SGP_WRITE )folio_mark_accessed (folio); -folio_put_swap (folio,NULL ); +folio_put_swap (folio);swap_cache_del_folio (folio);folio_mark_dirty (folio);put_swap_device (si);
mm/swap.h +15 -2
@@ -253,7 +253,8 @@ extern int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp);int folio_alloc_swap (struct folio *folio);int folio_dup_swap_pages (struct folio *folio,struct page *page,unsigned long nr_pages); -void folio_put_swap (struct folio *folio,struct page *page); +void folio_put_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages);/* For internal use */ extern void __swap_cluster_free_entries(struct swap_info_struct *si,
@@ -382,7 +383,8 @@ static inline int folio_dup_swap_pages(struct folio *folio, struct page *page,return -EINVAL ; } -static inline void folio_put_swap (struct folio *folio,struct page *page) +static inline void folio_put_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) { }
@@ -484,6 +486,17 @@ static inline int folio_dup_swap(struct folio *folio) folio_nr_pages(folio)); } +/** +* folio_put_swap() - Decrease swap count of all swap entries of a folio. +* @folio: folio with swap entries bound. +* +* See folio_put_swap_pages() for more information. +*/ +static inline void folio_put_swap (struct folio *folio) +{ +folio_put_swap_pages (folio,folio_page (folio,0 ),folio_nr_pages (folio)); +} +extern const struct swap_ops swap_bdev_ops; int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
mm/swapfile.c +8 -9
@@ -1817,27 +1817,25 @@ int folio_dup_swap_pages(struct folio *folio, struct page *page, }/** -* folio_put_swap() - Decrease swap count of swap entries of a folio. +* folio_put_swap_pages() - Decrease swap count of swap entries of a folio. * @folio: folio with swap entries bounded, must be in swap cache and locked. -* @page: if not NULL, only decrease the swap count of this page. +* @page: the first page in the folio to decrease the swap count for. +* @nr_pages: the number of pages in the folio to decrease the swap count for. * * This won't free the swap slots even if swap count drops to zero, they are * still pinned by the swap cache. User may call folio_free_swap to free them. * Context: Caller must ensure the folio is locked and in the swap cache. */ -void folio_put_swap (struct folio *folio,struct page *page) +void folio_put_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) {swp_entry_t entry = folio->swap; -unsigned long nr_pages =folio_nr_pages (folio);struct swap_info_struct *si =__swap_entry_to_info (entry);VM_WARN_ON_FOLIO (!folio_test_locked (folio), folio);VM_WARN_ON_FOLIO (!folio_test_swapcache (folio), folio); -if (page) { - entry.val +=folio_page_idx (folio, page); - nr_pages =1 ; - } + entry.val +=folio_page_idx (folio, page);swap_put_entries_cluster (si,swp_offset (entry), nr_pages, false); }
@@ -2570,7 +2568,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, setpte:set_pte_at (vma->vm_mm, addr, pte, new_pte); -folio_put_swap (swapcache,folio_file_page (swapcache,swp_offset (entry))); +folio_put_swap_pages (swapcache, +folio_file_page (swapcache,swp_offset (entry)),1 ); out:if (pte)pte_unmap_unlock (pte, ptl);
Signature · 1 line
2.43.0
Re: [PATCH 2/8] mm/swapfile: add batched version of folio_put_swap
Quoted 13 lines · Dev Jain
Add
folio_put_swap_pagesto handle a batch of consecutive pages. Note thatfolio_put_swapalready can handle a subset of this:nr_pages== 1 andnr_pages==folio_nr_pages(folio). Generalize this to anynr_pages.Currently we have a not-so-nice logic of passing in subpage == NULL if we mean to exercise the logic on the entire folio, and subpage != NULL if we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokesfolio_put_swap_pages()if it wants to operate on a range of pages in the folio (i.enr_pagesmay be anything between 1 andfolio_nr_pages()), and invokesfolio_put_swap()if it wants to operate on the entire folio.
Quoted 2 lines
Signed-off-by Dev Jain <[email protected]>
[...]
Quoted 16 lines
mm/memory.c +1
-1@@ -5198,7 +5198,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)if (unlikely (folio != swapcache)) {folio_add_new_anon_rmap (folio, vma, address,RMAP_EXCLUSIVE );folio_add_lru_vma (folio, vma); -folio_put_swap (swapcache,NULL ); +folio_put_swap (swapcache); }else if (!folio_test_anon (folio)) {/* * We currently only expect !anon folios that are fully @@ -5207,12 +5207,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)VM_WARN_ON_ONCE_FOLIO (folio_nr_pages (folio) != nr_pages, folio);
mm/memory.c vm_fault_t do_swap_page(struct vm_fault *vmf) · line 5215
Quoted 10 lines
mm/memory.c +2
-2VM_WARN_ON_ONCE_FOLIO (folio_mapped (folio), folio);folio_add_new_anon_rmap (folio, vma, address, rmap_flags); -folio_put_swap (folio,NULL ); +folio_put_swap (folio); }else {VM_WARN_ON_ONCE (nr_pages !=1 && nr_pages !=folio_nr_pages (folio));folio_add_anon_rmap_ptes (folio, page, nr_pages, vma, address, rmap_flags); -folio_put_swap (folio, nr_pages ==1 ? page :NULL ); +folio_put_swap_pages (folio, page, nr_pages);
Yes. In do_swap_page(), page points to the first page of the large folio.
if (folio_test_large(folio) && folio_test_swapcache(folio)) {
...
page = &folio->page;
}Quoted 25 lines
mm/swapfile.c +5
-4@@ -1817,27 +1817,25 @@ int folio_dup_swap_pages(struct folio *folio, struct page *page, }/** -* folio_put_swap() - Decrease swap count of swap entries of a folio. +* folio_put_swap_pages() - Decrease swap count of swap entries of a folio. * @folio: folio with swap entries bounded, must be in swap cache and locked. -* @page: if not NULL, only decrease the swap count of this page. +* @page: the first page in the folio to decrease the swap count for. +* @nr_pages: the number of pages in the folio to decrease the swap count for. * * This won't free the swap slots even if swap count drops to zero, they are * still pinned by the swap cache. User may call folio_free_swap to free them. * Context: Caller must ensure the folio is locked and in the swap cache. */ -void folio_put_swap (struct folio *folio,struct page *page) +void folio_put_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) {swp_entry_t entry = folio->swap; -unsigned long nr_pages =folio_nr_pages (folio);struct swap_info_struct *si =__swap_entry_to_info (entry);
mm/swapfile.c int folio_dup_swap_pages(struct folio *folio, struct page *page, · line 1840
Quoted 10 lines
mm/swapfile.c +1
-4VM_WARN_ON_FOLIO (!folio_test_locked (folio), folio);VM_WARN_ON_FOLIO (!folio_test_swapcache (folio), folio); -if (page) { - entry.val +=folio_page_idx (folio, page); - nr_pages =1 ; - } + entry.val +=folio_page_idx (folio, page);swap_put_entries_cluster (si,swp_offset (entry), nr_pages, false);
Maybe a guard against potential overflow would help? also in patch 1?
idx = folio_page_idx(folio, page);
VM_WARN_ON_FOLIO(idx + nr_pages > folio_nr_pages(folio), folio);
Best Regards
Barry
Re: [PATCH 2/8] mm/swapfile: add batched version of folio_put_swap
Quoted 14 lines · Barry Song
Quoted 13 lines · Dev Jain
Add
folio_put_swap_pagesto handle a batch of consecutive pages. Note thatfolio_put_swapalready can handle a subset of this:nr_pages== 1 andnr_pages==folio_nr_pages(folio). Generalize this to anynr_pages.Currently we have a not-so-nice logic of passing in subpage == NULL if we mean to exercise the logic on the entire folio, and subpage != NULL if we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokesfolio_put_swap_pages()if it wants to operate on a range of pages in the folio (i.enr_pagesmay be anything between 1 andfolio_nr_pages()), and invokesfolio_put_swap()if it wants to operate on the entire folio.
Quoted 4 lines
Quoted 2 lines
Signed-off-by Dev Jain <[email protected]>Reviewed-by Barry Song <[email protected]>
Thanks for your review.
Quoted 70 lines
[...]
Quoted 16 lines
mm/memory.c +1
-1@@ -5198,7 +5198,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)if (unlikely (folio != swapcache)) {folio_add_new_anon_rmap (folio, vma, address,RMAP_EXCLUSIVE );folio_add_lru_vma (folio, vma); -folio_put_swap (swapcache,NULL ); +folio_put_swap (swapcache); }else if (!folio_test_anon (folio)) {/* * We currently only expect !anon folios that are fully @@ -5207,12 +5207,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)VM_WARN_ON_ONCE_FOLIO (folio_nr_pages (folio) != nr_pages, folio);mm/memory.c vm_fault_t do_swap_page(struct vm_fault *vmf) · line 5215
Quoted 10 lines
mm/memory.c +2
-2VM_WARN_ON_ONCE_FOLIO (folio_mapped (folio), folio);folio_add_new_anon_rmap (folio, vma, address, rmap_flags); -folio_put_swap (folio,NULL ); +folio_put_swap (folio); }else {VM_WARN_ON_ONCE (nr_pages !=1 && nr_pages !=folio_nr_pages (folio));folio_add_anon_rmap_ptes (folio, page, nr_pages, vma, address, rmap_flags); -folio_put_swap (folio, nr_pages ==1 ? page :NULL ); +folio_put_swap_pages (folio, page, nr_pages);Yes. In
do_swap_page(),pagepoints to the first page of the large folio.if (folio_test_large(folio) && folio_test_swapcache(folio)) { ... page = &folio->page; }Quoted 34 lines
mm/swapfile.c +6
-8@@ -1817,27 +1817,25 @@ int folio_dup_swap_pages(struct folio *folio, struct page *page, }/** -* folio_put_swap() - Decrease swap count of swap entries of a folio. +* folio_put_swap_pages() - Decrease swap count of swap entries of a folio. * @folio: folio with swap entries bounded, must be in swap cache and locked. -* @page: if not NULL, only decrease the swap count of this page. +* @page: the first page in the folio to decrease the swap count for. +* @nr_pages: the number of pages in the folio to decrease the swap count for. * * This won't free the swap slots even if swap count drops to zero, they are * still pinned by the swap cache. User may call folio_free_swap to free them. * Context: Caller must ensure the folio is locked and in the swap cache. */ -void folio_put_swap (struct folio *folio,struct page *page) +void folio_put_swap_pages (struct folio *folio,struct page *page, +unsigned long nr_pages) {swp_entry_t entry = folio->swap; -unsigned long nr_pages =folio_nr_pages (folio);struct swap_info_struct *si =__swap_entry_to_info (entry);VM_WARN_ON_FOLIO (!folio_test_locked (folio), folio);VM_WARN_ON_FOLIO (!folio_test_swapcache (folio), folio); -if (page) { - entry.val +=folio_page_idx (folio, page); - nr_pages =1 ; - } + entry.val +=folio_page_idx (folio, page);
Quoted 7 lines
mm/swapfile.c int folio_dup_swap_pages(struct folio *folio, struct page *page, · line 1840
Quoted 1 line
mm/swapfile.c +0
-0swap_put_entries_cluster (si,swp_offset (entry), nr_pages, false);Maybe a guard against potential overflow would help? also in patch 1?
idx =
folio_page_idx(folio, page);
VM_WARN_ON_FOLIO(idx + nr_pages > folio_nr_pages(folio), folio);
We had this discussion before and I am struggling to recall that - I think there are currently both cases, the batched helpers not doing the sanity checking but documenting it (I haven't documented it in this one, and in set_softleaf_ptes too, will audit later), or doing the sanity checking.
But I also recall the expectation is that CONFIG_DEBUG_VM is not used in production kernels, so I can put this in v2.
Quoted 3 lines
Best Regards
Barry
PATCH 3/8 mm/rmap: mm/rmap: Add batched version of folio_try_share_anon_rmap_pte
In reply to Dev JainTo enable batched unmapping of anonymous folios, we need to handle the sharing of exclusive pages. Hence, a batched version of folio_try_share_anon_rmap_pte is required.
Currently, the sole purpose of nr_pages in __folio_try_share_anon_rmap is to do some rmap sanity checks. Now, clear the PageAnonExclusive bit on a batch of nr_pages. Refactor the function such that the clearing of the bit can be done at one place without duplication.
Note that __folio_try_share_anon_rmap can receive nr_pages == HPAGE_PMD_NR from the PMD path, but currently we only clear the bit on the head page. Retain this behaviour by setting nr_pages = 1 in case the caller is folio_try_share_anon_rmap_pmd.
While at it, convert nr_pages to unsigned long to future-proof from overflow in case P4D-huge mappings etc get supported down the road. I haven't made such a change in each function receiving nr_pages in try_to_unmap_one - perhaps this can be done incrementally.
--- include/linux/rmap.h | 51 +++++++++++++++++++++++++++++--------------- 1 file changed, 34 insertions(+), 17 deletions(-)
include/linux/rmap.h +34 -17
@@ -706,17 +706,18 @@ static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio, } static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, -struct page *page,int nr_pages,enum pgtable_level level) +struct page *page,unsigned long nr_pages,enum pgtable_level level) { +/* device private folios cannot get pinned via GUP. */ +const bool pinnable = !folio_is_device_private (folio); +VM_WARN_ON_FOLIO (!folio_test_anon (folio), folio);VM_WARN_ON_FOLIO (!PageAnonExclusive (page), folio);__folio_rmap_sanity_checks (folio, page, nr_pages, level); -/* device private folios cannot get pinned via GUP. */ -if (unlikely (folio_is_device_private (folio))) { -ClearPageAnonExclusive (page); -return 0 ; - } +/* We only clear anon-exclusive from head page of PMD folio. */ +if (level ==PGTABLE_LEVEL_PMD ) + nr_pages =1 ;/* * We have to make sure that when we clear PageAnonExclusive, that
@@ -760,29 +761,38 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio,* so we use explicit ones here. */ -/* Paired with the memory barrier in try_grab_folio(). */ -if (IS_ENABLED (CONFIG_HAVE_GUP_FAST )) -smp_mb (); +if (likely (pinnable)) { +/* Paired with the memory barrier in try_grab_folio(). */ +if (IS_ENABLED (CONFIG_HAVE_GUP_FAST )) +smp_mb (); -if (unlikely (folio_maybe_dma_pinned (folio))) -return -EBUSY ; -ClearPageAnonExclusive (page); +if (unlikely (folio_maybe_dma_pinned (folio))) +return -EBUSY ; + } + +for (;;) { +ClearPageAnonExclusive (page); +if (--nr_pages ==0 ) +break ; + page++; + }/* * This is conceptually a smp_wmb() paired with the smp_rmb() in * gup_must_unshare(). */ -if (IS_ENABLED (CONFIG_HAVE_GUP_FAST )) +if (likely (pinnable) &&IS_ENABLED (CONFIG_HAVE_GUP_FAST ))smp_mb__after_atomic ();return 0 ; }/** -* folio_try_share_anon_rmap_pte - try marking an exclusive anonymous page -* mapped by a PTE possibly shared to prepare +* folio_try_share_anon_rmap_ptes - try marking exclusive anonymous pages +* mapped by PTEs possibly shared to prepare * for KSM or temporary unmapping * @folio: The folio to share a mapping of -* @page: The mapped exclusive page +* @page: The first mapped exclusive page of the batch in the folio +* @nr_pages: The number of pages to share in the folio (batch size) * * The caller needs to hold the page table lock and has to have the page table * entries cleared/invalidated.
@@ -798,10 +808,17 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio,* Returns 0 if marking the mapped page possibly shared succeeded. Returns * -EBUSY otherwise. */ +static inline int folio_try_share_anon_rmap_ptes (struct folio *folio, +struct page *page,unsigned long nr_pages) +{ +return __folio_try_share_anon_rmap (folio, page, nr_pages, +PGTABLE_LEVEL_PTE ); +} +static inline int folio_try_share_anon_rmap_pte (struct folio *folio,struct page *page) { -return __folio_try_share_anon_rmap (folio, page,1 ,PGTABLE_LEVEL_PTE ); +return folio_try_share_anon_rmap_ptes (folio, page,1 ); }/**
Signature · 1 line
2.43.0
PATCH 4/8 mm/internal: rename swap offset helpers to softleaf offset
In reply to Dev JainIn preparation for adding a helper to set softleaf ptes in one go, generalize the swap entry helpers shifting the swap offset by delta, for softleaves.
Note that the soft-dirty bit, exclusive bit and uffd bit preservation will still work for non-swap softleaves, since a softleaf entry is constructed out of a type and offset, and those bits are ahead of the soft-dirty, exclusive and uffd bits.
For example, for a migration entry, pte_swp_exclusive() will return false, as the exclusivity is encoded in the type itself (SOFTLEAF_MIGRATION_READ_EXCLUSIVE).
--- mm/internal.h | 29 +++++++++++++++-------------- mm/memory.c | 4 ++-- 2 files changed, 17 insertions(+), 16 deletions(-)
mm/internal.h +15 -14
@@ -475,16 +475,16 @@ unsigned int folio_pte_batch(struct folio *folio, pte_t *ptep, pte_t pte, unsigned int max_nr);/** -* pte_move_swp_offset - Move the swap entry offset field of a swap pte -* forward or backward by delta -* @pte: The initial pte state; must be a swap entry +* pte_move_softleaf_offset - Move the softleaf entry offset field of a +* softleaf pte forward or backward by delta +* @pte: The initial pte state; must be a softleaf entry * @delta: The direction and the offset we are moving; forward if delta * is positive; backward if delta is negative * -* Moves the swap offset, while maintaining all other fields, including -* swap type, and any swp pte bits. The resulting pte is returned. +* Moves the softleaf offset, while maintaining all other fields, including +* softleaf type, and any softleaf pte bits. The resulting pte is returned. */ -static inline pte_t pte_move_swp_offset (pte_t pte,long delta) +static inline pte_t pte_move_softleaf_offset (pte_t pte,long delta) {const softleaf_t entry =softleaf_from_pte (pte); pte_t new = __swp_entry_to_pte(__swp_entry(swp_type(entry),
@@ -502,15 +502,16 @@ static inline pte_t pte_move_swp_offset(pte_t pte, long delta)/** -* pte_next_swp_offset - Increment the swap entry offset field of a swap pte. -* @pte: The initial pte state; must be a swap entry. +* pte_next_softleaf_offset - Increment the softleaf entry offset field of a +* non-present pte. +* @pte: The initial pte state; must be a softleaf entry. * -* Increments the swap offset, while maintaining all other fields, including -* swap type, and any swp pte bits. The resulting pte is returned. +* Increments the softleaf offset, while maintaining all other fields, including +* softleaf type, and any softleaf pte bits. The resulting pte is returned. */ -static inline pte_t pte_next_swp_offset (pte_t pte) +static inline pte_t pte_next_softleaf_offset (pte_t pte) { -return pte_move_swp_offset (pte,1 ); +return pte_move_softleaf_offset (pte,1 ); }/**
@@ -530,7 +531,7 @@ static inline pte_t pte_next_swp_offset(pte_t pte)*/ static inline int swap_pte_batch (pte_t *start_ptep,int max_nr,pte_t pte) { -pte_t expected_pte =pte_next_swp_offset (pte); +pte_t expected_pte =pte_next_softleaf_offset (pte);const pte_t *end_ptep = start_ptep + max_nr;pte_t *ptep = start_ptep +1 ;
@@ -542,7 +543,7 @@ static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte)if (!pte_same (pte, expected_pte))break ; - expected_pte =pte_next_swp_offset (expected_pte); + expected_pte =pte_next_softleaf_offset (expected_pte); ptep++; }
mm/memory.c +2 -2
@@ -4753,7 +4753,7 @@ static bool can_swapin_thp(struct vm_fault *vmf, pte_t *ptep, int nr_pages) idx = (vmf->address - addr) /PAGE_SIZE ; pte =ptep_get (ptep); -if (!pte_same (pte,pte_move_swp_offset (vmf->orig_pte, -idx))) +if (!pte_same (pte,pte_move_softleaf_offset (vmf->orig_pte, -idx)))return false;/* * swap_read_folio() can't handle the case a large folio is hybridly
@@ -5062,7 +5062,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) folio_ptep = vmf->pte - idx; folio_pte =ptep_get (folio_ptep); -if (!pte_same (folio_pte,pte_move_swp_offset (vmf->orig_pte, -idx)) || +if (!pte_same (folio_pte,pte_move_softleaf_offset (vmf->orig_pte, -idx)) ||swap_pte_batch (folio_ptep, nr, folio_pte) != nr) goto check_folio;
Signature · 1 line
2.43.0
PATCH 5/8 mm/internal: add set_softleaf_ptes
In reply to Dev JainCurrently we have a helper called set_ptes() which is used to set consecutive present ptes in the pgtables. To do the same operation but to set "consecutive" nonpresent (softleaf) ptes, add set_softleaf_ptes().
The softleaves which have a notion of consecutivity is swap softleaf, and those grouped by softeaf_has_pfn(). The latter is trivial; future code can convert present ptes pointing to the same large folio to swap softleaves with consecutive offsets using this helper.
The other case is softleaf markers. They do not have a notion of a swap offset or PFN, so future code can use set_softleaf_ptes() to store multiple (same) markers on the ptes.
--- mm/internal.h | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)
mm/internal.h +33 -0
@@ -514,6 +514,39 @@ static inline pte_t pte_next_softleaf_offset(pte_t pte)return pte_move_softleaf_offset (pte,1 ); } +/** +* set_softleaf_ptes - Set consecutive softleaf PTEs. +* @mm: Address space the PTEs belong to. +* @addr: Address of the first PTE. +* @ptep: Page table pointer for the first PTE. +* @pte: PTE to set for the first entry. +* @nr: Number of PTEs to set. +* +* Install @nr softleaf PTEs, advancing @pte when its softleaf entry +* represents consecutive offsets. Swap entries advance through swap offsets, +* PFN softleaf entries advance through PFNs (encoded by swap offset), and +* marker entries are repeated unchanged. +*/ +static inline void set_softleaf_ptes (struct mm_struct *mm,unsigned long addr, +pte_t *ptep,pte_t pte,unsigned long nr) +{ +softleaf_t entry; +bool advance; + + entry =softleaf_from_pte (pte); + advance =softleaf_is_swap (entry) ||softleaf_has_pfn (entry); + +for (;;) { +set_pte_at (mm, addr, ptep, pte); +if (--nr ==0 ) +break ; +if (advance) + pte =pte_next_softleaf_offset (pte); + ptep++; + addr +=PAGE_SIZE ; + } +} +/** * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries * @start_ptep: Page table pointer for the first entry.
Signature · 1 line
2.43.0
PATCH 6/8 mm/memory: use set_softleaf_ptes for uffd-wp markers
In reply to Dev JainUse set_softleaf_ptes() to store multiple uffd-wp marker entries instead of open coding the batched setting.
--- mm/memory.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)
mm/memory.c +2 -8
@@ -1733,14 +1733,8 @@ bool cond_install_uffd_wp_ptes(struct vm_area_struct *vma,if (likely (!arm_uffd_pte))return false; -for (;;) { -set_pte_at (vma->vm_mm, addr, ptep, -make_pte_marker (PTE_MARKER_UFFD_WP )); -if (--nr_ptes ==0 ) -break ; - ptep++; - addr +=PAGE_SIZE ; - } +set_softleaf_ptes (vma->vm_mm, addr, ptep, +make_pte_marker (PTE_MARKER_UFFD_WP ), nr_ptes);return true; }
Signature · 1 line
2.43.0
PATCH 7/8 mm: move anon-exclusive batch helper to internal.h
In reply to Dev JainIn preparation for optimizing large folio unmapping, we need to reuse the page_anon_exclusive_batch helper in rmap.c. Therefore, move it from mprotect.c to internal.h.
--- mm/internal.h | 17 +++++++++++++++++ mm/mprotect.c | 17 ----------------- 2 files changed, 17 insertions(+), 17 deletions(-)
mm/internal.h +17 -0
@@ -474,6 +474,23 @@ static inline unsigned int folio_pte_batch_flags(struct folio *folio,unsigned int folio_pte_batch (struct folio *folio,pte_t *ptep,pte_t pte,unsigned int max_nr); +/* +* Get max length of consecutive PTEs pointing to PageAnonExclusive() pages or +* !PageAnonExclusive() pages, starting from start_idx. Caller must enforce +* that the PTEs point to consecutive pages of the same anon large folio. +*/ +static __always_inline int page_anon_exclusive_batch(int start_idx, int max_len, +struct page *first_page,bool expected_anon_exclusive) +{ +int idx; + +for (idx = start_idx +1 ; idx < start_idx + max_len; ++idx) { +if (expected_anon_exclusive !=PageAnonExclusive (first_page + idx)) +break ; + } +return idx - start_idx; +} +/** * pte_move_softleaf_offset - Move the softleaf entry offset field of a * softleaf pte forward or backward by delta
mm/mprotect.c +0 -17
@@ -138,23 +138,6 @@ static __always_inline void prot_commit_flush_ptes(struct vm_area_struct *vma,tlb_flush_pte_range (tlb, addr, nr_ptes *PAGE_SIZE ); } -/* -* Get max length of consecutive ptes pointing to PageAnonExclusive() pages or -* !PageAnonExclusive() pages, starting from start_idx. Caller must enforce -* that the ptes point to consecutive pages of the same anon large folio. -*/ -static __always_inline int page_anon_exclusive_batch(int start_idx, int max_len, -struct page *first_page,bool expected_anon_exclusive) -{ -int idx; - -for (idx = start_idx +1 ; idx < start_idx + max_len; ++idx) { -if (expected_anon_exclusive !=PageAnonExclusive (first_page + idx)) -break ; - } -return idx - start_idx; -} -/* * This function is a result of trying our very best to retain the * "avoid the write-fault handler" optimization. In can_change_pte_writable(),
Signature · 1 line
2.43.0
PATCH 8/8 mm/rmap: batch unmap anonymous swap-backed large folios
In reply to Dev JainEnable batch clearing of ptes, and batch swap setting of ptes for anon swap-backed folio unmapping.
Processing all ptes of a large folio in one go helps us batch across atomics (add_mm_counter etc), barriers (in the function __folio_try_share_anon_rmap), repeated calls to page_vma_mapped_walk(), to name a few. In general, batching helps us to execute similar code together, making the execution of the program more memory and CPU friendly.
On arm64-contpte, batching also helps us avoid redundant ptep_get() calls and TLB flushes while breaking the contpte mapping.
The handling of anon-exclusivity is very similar to commit cac1db8c3aad ("mm: optimize mprotect() by PTE batching"). Since folio_unmap_pte_batch() won't look at the bits of the underlying page, we need to process sub-batches of ptes pointing to pages which are same w.r.t exclusivity, and batch set only those ptes to swap ptes in one go.
arch_unmap_one() is only defined for sparc64; I am not comfortable regarding the nuances between retrieving the pfn from pte_pfn() or from (paddr = pte_val(oldpte) & _PAGE_PADDR_4V).
(And, pte_next_pfn() can't even be called from arch_unmap_one() because that file does not include pgtable.h) So just disable the "sparc64-anon-swapbacked" case for now.
We need to take care of rmap accounting (folio_remove_rmap_ptes) and reference accounting (folio_put_refs) when anon folio unmap succeeds. In case we partially batch the large folio and fail, we need to correctly do the accounting for pages which were successfully unmapped. So, put this accounting code (which is finish_folio_unmap()) in __ttu_anon_swapbacked_folio() itself, instead of doing some horrible goto jumping at the callsite of ttu_anon_folio().
Similarly, do the finish_folio_unmap() in ttu_anon_folio itself for the non-swapbacked (lazyfree) case.
If the batch length is less than the number of pages in the folio, then we must skip over this batch.
The page_vma_mapped_walk API ensures this - check_pte() will return true only if any of [pvmw->pfn, pvmw->pfn + nr_pages) is mapped by the pte. There is no pfn underlying a swap pte, so check_pte returns false and we keep skipping until we hit a present pte, which is where we want to start unmapping from next.
Remove the label finish_unmap since no goto callers are left now.
--- mm/rmap.c | 109 +++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 80 insertions(+), 29 deletions(-)
mm/rmap.c +80 -29
@@ -1964,11 +1964,11 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, end_addr =pmd_addr_end (addr, vma->vm_end); max_nr = (end_addr - addr) >>PAGE_SHIFT ; -/* We only support lazyfree or file folios batching for now ... */ -if (folio_test_anon (folio) &&folio_test_swapbacked (folio)) +if (pte_unused (pte))return 1 ; -if (pte_unused (pte)) +if (__is_defined (__HAVE_ARCH_UNMAP_ONE) &&folio_test_anon (folio) && +folio_test_swapbacked (folio))return 1 ;/*
@@ -2139,16 +2139,25 @@ static pte_t swp_pte_prepare(swp_entry_t entry, pte_t old_pte,return swp_pte; } -static bool ttu_anon_swapbacked_folio (struct vm_area_struct *vma, +static void finish_folio_unmap (struct vm_area_struct *vma, +struct folio *folio,struct page *page,unsigned long nr_pages) +{ +folio_remove_rmap_ptes (folio, page, nr_pages, vma); +if (vma->vm_flags &VM_LOCKED ) +mlock_drain_local (); +folio_put_refs (folio, nr_pages); +} + +static bool __ttu_anon_swapbacked_folio (struct vm_area_struct *vma,struct folio *folio,struct page *page,unsigned long address, -pte_t *ptep,pte_t pteval) +pte_t *ptep,pte_t pteval,unsigned long nr_pages, +bool anon_exclusive) { -const bool anon_exclusive =folio_test_anon (folio) && -PageAnonExclusive (page);swp_entry_t entry =page_swap_entry (page);struct mm_struct *mm = vma->vm_mm; +pte_t swp_pte; -if (folio_dup_swap_pages (folio, page,1 ) <0 ) +if (folio_dup_swap_pages (folio, page, nr_pages) <0 )return false;/*
@@ -2157,21 +2166,57 @@ static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,* so we'll not check/care. */ if (arch_unmap_one (mm, vma, address, pteval) <0 ) { -folio_put_swap_pages (folio, page,1 ); +VM_WARN_ON (nr_pages !=1 ); +folio_put_swap_pages (folio, page, nr_pages);return false; }/* See folio_try_share_anon_rmap(): clear PTE first. */ -if (anon_exclusive &&folio_try_share_anon_rmap_pte (folio, page)) { -folio_put_swap_pages (folio, page,1 ); +if (anon_exclusive && +folio_try_share_anon_rmap_ptes (folio, page, nr_pages)) { +folio_put_swap_pages (folio, page, nr_pages);return false; }mm_prepare_for_swap_entries (mm); -dec_mm_counter (mm,MM_ANONPAGES ); -inc_mm_counter (mm,MM_SWAPENTS ); -set_pte_at (mm, address, ptep, -swp_pte_prepare (entry, pteval, anon_exclusive)); +add_mm_counter (mm,MM_ANONPAGES , -nr_pages); +add_mm_counter (mm,MM_SWAPENTS , nr_pages); + swp_pte =swp_pte_prepare (entry, pteval, anon_exclusive); +set_softleaf_ptes (mm, address, ptep, swp_pte, nr_pages); +finish_folio_unmap (vma, folio, page, nr_pages); +return true; +} + +static bool ttu_anon_swapbacked_folio (struct vm_area_struct *vma, +struct folio *folio,struct page *first_page, +unsigned long address,pte_t *ptep,pte_t pteval, +unsigned long nr_pages) +{ +unsigned long batch_idx =0 ; + +while (nr_pages) { +bool anon_exclusive =PageAnonExclusive (first_page + batch_idx); +unsigned long len =page_anon_exclusive_batch (batch_idx, + nr_pages, first_page, anon_exclusive); + +if (!__ttu_anon_swapbacked_folio (vma, folio, + first_page + batch_idx, address, ptep, pteval, + len, anon_exclusive)) { +/* Restore the remaining PTEs that were cleared. */ +set_ptes (vma->vm_mm, address, ptep, pteval, nr_pages); +return false; + } + + nr_pages -= len; +if (!nr_pages) +break ; + + pteval =pte_advance_pfn (pteval, len); + address += len *PAGE_SIZE ; + batch_idx += len; + ptep += len; + } +return true; }
@@ -2184,15 +2229,22 @@ static bool ttu_anon_folio(struct vm_area_struct *vma, struct folio *folio,* See handle_pte_fault() ... */ if (WARN_ON_ONCE (folio_test_swapbacked (folio) != -folio_test_swapcache (folio))) +folio_test_swapcache (folio))) { +set_ptes (vma->vm_mm, address, ptep, pteval, nr_pages);return false; + } -if (!folio_test_swapbacked (folio)) -return ttu_anon_lazyfree_folio (vma, folio, nr_pages); +if (!folio_test_swapbacked (folio)) { +if (!ttu_anon_lazyfree_folio (vma, folio, nr_pages)) { +set_ptes (vma->vm_mm, address, ptep, pteval, nr_pages); +return false; + } +finish_folio_unmap (vma, folio, page, nr_pages); +return true; + } -/* nr_pages > 1 not supported yet */ return ttu_anon_swapbacked_folio (vma, folio, page, address, ptep, - pteval); + pteval, nr_pages); }/*
@@ -2373,13 +2425,15 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,*/ dec_mm_counter (mm,mm_counter (folio)); }else if (folio_test_anon (folio)) { + +/* finish_folio_unmap handled internally */ if (!ttu_anon_folio (vma, folio, page, address, - pvmw.pte, pteval, nr_pages)) { -set_ptes (mm, address, pvmw.pte, pteval, nr_pages); + pvmw.pte, pteval, nr_pages)) goto walk_abort; - } - goto finish_unmap; +if (nr_pages ==folio_nr_pages (folio)) + goto walk_done; +continue ; }else {/* * This is a locked file-backed folio,
@@ -2394,11 +2448,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,*/ add_mm_counter (mm,mm_counter_file (folio), -nr_pages); } -finish_unmap: -folio_remove_rmap_ptes (folio, page, nr_pages, vma); -if (vma->vm_flags &VM_LOCKED ) -mlock_drain_local (); -folio_put_refs (folio, nr_pages); + +finish_folio_unmap (vma, folio, page, nr_pages);/* * If we are sure that we batched the entire folio and cleared
Signature · 1 line
2.43.0
Quoted 68 lines · Dev Jain
Speed up unmapping of anonymous swapbacked large folios by clearing the ptes, and setting swap ptes, in one go.
The following benchmark (stolen from Barry) is used to measure the time taken to swapout 256M worth of memory backed by 64K large folios:
#define
_GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>#define
SIZE_MB256
#defineSIZE_BYTES(SIZE_MB* 1024 * 1024)int main() { void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (addr == MAP_FAILED) { perror("mmap failed"); return 1; } memset(addr, 0, SIZE_BYTES); struct timespec start, end; clock_gettime(CLOCK_MONOTONIC, &start); if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) { perror("madvise(MADV_PAGEOUT) failed"); munmap(addr, SIZE_BYTES); return 1; } clock_gettime(CLOCK_MONOTONIC, &end); long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 + (end.tv_nsec - start.tv_nsec); printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n", duration_ns, duration_ns / 1e6); munmap(addr, SIZE_BYTES); return 0;}
Performance as measured on a Linux VM on Apple M3 (arm64):
Vanilla - Mean: 37401913 ns, std dev: 12%
Patched - Mean: 17420282 ns, std dev: 11%resulting in more than 2x speedup.
No regression observed on 4K folios.
Performance as measured on bare metal x86:
Vanilla - mean: 54986286 ns, std dev: 1.5%
Patched - mean: 51930795 ns, std dev: 3%I tried magnifying the difference on x86 by using 1M large folios, but can't spot an obvious improvement (looks like my system is too fast to benefit from batched atomic operations!), hinting that the benefit lies mainly in the reduction of
ptep_get()calls and the reduction of TLB flushes during contpte-unfolding, on arm64.
Quoted 4 lines
No regression is observed on 4K folios on x86 too.
---
Sashiko:
Patch 1: at that point there is no caller passing 1 < nr_pages < folio_nr_pages to folio_dup_swap_pages(), so doesn't apply.
Patch 3:
a) yes I can add a sanity check here, something like VM_WARN_ON_ONCE(page_anon_exclusive_batch != nr_pages).
b) There is no caller passing level == PGTABLE_LEVEL_PUD, but for future-proofing I can change this to level != PGTABLE_LEVEL_PTE.
Patch 8:
the is_defined() thingy is wrong, I'll change that. This was pointed out before too, but in between splitting that series into multiple sub-series, I forgot to incorporate this change, sorry.
Quoted 68 lines · Dev Jain
Speed up unmapping of anonymous swapbacked large folios by clearing the ptes, and setting swap ptes, in one go.
The following benchmark (stolen from Barry) is used to measure the time taken to swapout 256M worth of memory backed by 64K large folios:
#define
_GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>#define
SIZE_MB256
#defineSIZE_BYTES(SIZE_MB* 1024 * 1024)int main() { void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (addr == MAP_FAILED) { perror("mmap failed"); return 1; } memset(addr, 0, SIZE_BYTES); struct timespec start, end; clock_gettime(CLOCK_MONOTONIC, &start); if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) { perror("madvise(MADV_PAGEOUT) failed"); munmap(addr, SIZE_BYTES); return 1; } clock_gettime(CLOCK_MONOTONIC, &end); long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 + (end.tv_nsec - start.tv_nsec); printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n", duration_ns, duration_ns / 1e6); munmap(addr, SIZE_BYTES); return 0;}
Performance as measured on a Linux VM on Apple M3 (arm64):
Vanilla - Mean: 37401913 ns, std dev: 12%
Patched - Mean: 17420282 ns, std dev: 11%resulting in more than 2x speedup.
No regression observed on 4K folios.
Performance as measured on bare metal x86:
Vanilla - mean: 54986286 ns, std dev: 1.5%
Patched - mean: 51930795 ns, std dev: 3%I tried magnifying the difference on x86 by using 1M large folios, but can't spot an obvious improvement (looks like my system is too fast to benefit from batched atomic operations!), hinting that the benefit lies mainly in the reduction of
ptep_get()calls and the reduction of TLB flushes during contpte-unfolding, on arm64.
Quoted 3 lines
No regression is observed on 4K folios on x86 too.
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Hi Andrew,
I am not sure what is the current process in mm regarding sending patches during merge window - would you prefer seeing v2 after merge window or shall I respin?
David Hildenbrand (Arm)
maintainerQuoted 73 lines · Dev Jain
Quoted 70 lines · Dev Jain
Speed up unmapping of anonymous swapbacked large folios by clearing the ptes, and setting swap ptes, in one go.
The following benchmark (stolen from Barry) is used to measure the time taken to swapout 256M worth of memory backed by 64K large folios:
#define
_GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>#define
SIZE_MB256
#defineSIZE_BYTES(SIZE_MB* 1024 * 1024)int main() { void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (addr == MAP_FAILED) { perror("mmap failed"); return 1; } memset(addr, 0, SIZE_BYTES); struct timespec start, end; clock_gettime(CLOCK_MONOTONIC, &start); if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) { perror("madvise(MADV_PAGEOUT) failed"); munmap(addr, SIZE_BYTES); return 1; } clock_gettime(CLOCK_MONOTONIC, &end); long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 + (end.tv_nsec - start.tv_nsec); printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n", duration_ns, duration_ns / 1e6); munmap(addr, SIZE_BYTES); return 0;}
Performance as measured on a Linux VM on Apple M3 (arm64):
Vanilla - Mean: 37401913 ns, std dev: 12%
Patched - Mean: 17420282 ns, std dev: 11%resulting in more than 2x speedup.
No regression observed on 4K folios.
Performance as measured on bare metal x86:
Vanilla - mean: 54986286 ns, std dev: 1.5%
Patched - mean: 51930795 ns, std dev: 3%I tried magnifying the difference on x86 by using 1M large folios, but can't spot an obvious improvement (looks like my system is too fast to benefit from batched atomic operations!), hinting that the benefit lies mainly in the reduction of
ptep_get()calls and the reduction of TLB flushes during contpte-unfolding, on arm64.No regression is observed on 4K folios on x86 too.
Quoted 9 lines
Quoted 1 line
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Hi Andrew,
I am not sure what is the current process in mm regarding sending patches during merge window - would you prefer seeing v2 after merge window or shall I respin?
Let's wait for more review first. Most of the patches have not been reviewed and there is no time to rush at this point.
Signature · 3 lines
Cheers, David