mm-swap-cache-maximum-swapfile-size-when-init-swap.patch removed from -mm tree

The quilt patch titled
Subject: mm/swap: cache maximum swapfile size when init swap
has been removed from the -mm tree. Its filename was
mm-swap-cache-maximum-swapfile-size-when-init-swap.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Peter Xu <[email protected]>
Subject: mm/swap: cache maximum swapfile size when init swap
Date: Thu, 11 Aug 2022 12:13:30 -0400

We used to have swapfile_maximum_size() fetching a maximum value of swapfile size per-arch.

As the caller of max_swapfile_size() grows, this patch introduce a variable "swapfile_maximum_size" and cache the value of old max_swapfile_size(), so that we don't need to calculate the value every time.

Caching the value in swapfile_init() is safe because when reaching the phase we should have initialized all the relevant information. Here the major arch to take care of is x86, which defines the max swapfile size based on L1TF mitigation.

Here both X86_BUG_L1TF or l1tf_mitigation should have been setup properly when reaching swapfile_init(). As a reference, the code path looks like this for x86:

- start_kernel
- setup_arch
- early_cpu_init
- early_identify_cpu --> setup X86_BUG_L1TF
- parse_early_param
- l1tf_cmdline --> set l1tf_mitigation
- check_bugs
- l1tf_select_mitigation --> set l1tf_mitigation
- arch_call_rest_init
- rest_init
- kernel_init
- kernel_init_freeable
- do_basic_setup
- do_initcalls --> calls swapfile_init() (initcall level 4)

The swapfile size only depends on swp pte format on non-x86 archs, so caching it is safe too.

Since at it, rename max_swapfile_size() to arch_max_swapfile_size() because arch can define its own function, so it's more straightforward to have "arch_" as its prefix. At the meantime, export swapfile_maximum_size to replace the old usages of max_swapfile_size().

---

 arch/x86/mm/init.c       |    2 +-
 include/linux/swapfile.h |    5 ++++-
 include/linux/swapops.h  |    2 +-
 mm/swapfile.c            |    7 +++++--
 4 files changed, 11 insertions(+), 5 deletions(-)

@@ -1054,7 +1054,7 @@ void update_cache_mode_entry(unsigned en
 }
 
 #ifdef CONFIG_SWAP
-unsigned long max_swapfile_size(void)
+unsigned long arch_max_swapfile_size(void)
 {
 	unsigned long pages;
 

@@ -8,6 +8,9 @@
  */
 extern struct swap_info_struct *swap_info[];
 extern unsigned long generic_max_swapfile_size(void);
-extern unsigned long max_swapfile_size(void);
+unsigned long arch_max_swapfile_size(void);
+
+/* Maximum swapfile size supported for the arch (not inclusive). */
+extern unsigned long swapfile_maximum_size;
 
 #endif /* _LINUX_SWAPFILE_H */

@@ -307,7 +307,7 @@ static inline bool migration_entry_suppo
 	 * the offset large enough to cover all of them (PFN, A & D bits).
 	 */
 #ifdef CONFIG_SWAP
-	return max_swapfile_size() >= (1UL << SWP_MIG_TOTAL_BITS);
+	return swapfile_maximum_size >= (1UL << SWP_MIG_TOTAL_BITS);
 #else  /* CONFIG_SWAP */
 	return false;
 #endif	/* CONFIG_SWAP */

@@ -63,6 +63,7 @@ EXPORT_SYMBOL_GPL(nr_swap_pages);
 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
 long total_swap_pages;
 static int least_priority = -1;
+unsigned long swapfile_maximum_size;
 
 static const char Bad_file[] = "Bad swap file entry ";
 static const char Unused_file[] = "Unused swap file entry ";

@@ -2816,7 +2817,7 @@ unsigned long generic_max_swapfile_size(
 }
 
 /* Can be overridden by an architecture for additional checks. */
-__weak unsigned long max_swapfile_size(void)
+__weak unsigned long arch_max_swapfile_size(void)
 {
 	return generic_max_swapfile_size();
 }

@@ -2856,7 +2857,7 @@ static unsigned long read_swap_header(st
 	p->cluster_next = 1;
 	p->cluster_nr = 0;
 
-	maxpages = max_swapfile_size();
+	maxpages = swapfile_maximum_size;
 	last_page = swap_header->info.last_page;
 	if (!last_page) {
 		pr_warn("Empty swap-file\n");

@@ -3677,6 +3678,8 @@ static int __init swapfile_init(void)
 	for_each_node(nid)
 		plist_head_init(&swap_avail_heads[nid]);
 
+	swapfile_maximum_size = arch_max_swapfile_size();
+
 	return 0;
 }
 subsys_initcall(swapfile_init);

_

Patches currently in -mm which might be from [email protected] are