Skip to contentSkip to conversation

mm: Save soft-dirty bits on file pages

PATCH In review Cyrill Gorcunov 4 participants 15 messages Jul 26, 2013 – Jul 29, 2013

Subsystems (6)
Memory management x86 MM core Proc filesystem +2 more subsystems
lore
Share & tools
lore

Cyrill Gorcunov

author
#0 lore raw

PATCH 1/1 mm: Save soft-dirty bits on file pages

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Reported-by Andy Lutomirski <[email protected]>
Signed-off-by Cyrill Gorcunov <[email protected]>
Cc Pavel Emelyanov <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Matt Mackall <[email protected]>
Cc Xiao Guangrong <[email protected]>
Cc Marcelo Tosatti <[email protected]>
Cc KOSAKI Motohiro <[email protected]>
Cc Stephen Rothwell <[email protected]>
---
 arch/x86/include/asm/pgtable-2level.h |   48 +++++++++++++++++++++++++++++++++-
 arch/x86/include/asm/pgtable-3level.h |    3 ++
 arch/x86/include/asm/pgtable.h        |   15 ++++++++++
 arch/x86/include/asm/pgtable_types.h  |    4 ++
 fs/proc/task_mmu.c                    |    2 +
 mm/fremap.c                           |   14 +++++++--
 mm/memory.c                           |   20 +++++++++++---
 mm/rmap.c                             |   10 +++++--
 8 files changed, 105 insertions(+), 11 deletions(-)
arch/x86/include/asm/pgtable-2level.h +47 -1
Index: linux-2.6.git/arch/x86/include/asm/pgtable-2level.h
===================================================================
@@ -55,9 +55,53 @@ static inline pmd_t native_pmdp_get_and_
 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
 #endif
 
+#ifdef CONFIG_MEM_SOFT_DIRTY
+
+/*
+ * Bits _PAGE_BIT_PRESENT, _PAGE_BIT_FILE, _PAGE_BIT_SOFT_DIRTY and
+ * _PAGE_BIT_PROTNONE are taken, split up the 28 bits of offset
+ * into this range.
+ */
+#define PTE_FILE_MAX_BITS	28
+#define PTE_FILE_SHIFT1		(_PAGE_BIT_PRESENT + 1)
+#define PTE_FILE_SHIFT2		(_PAGE_BIT_FILE + 1)
+#define PTE_FILE_SHIFT3		(_PAGE_BIT_PROTNONE + 1)
+#define PTE_FILE_SHIFT4		(_PAGE_BIT_SOFT_DIRTY + 1)
+#define PTE_FILE_BITS1		(PTE_FILE_SHIFT2 - PTE_FILE_SHIFT1 - 1)
+#define PTE_FILE_BITS2		(PTE_FILE_SHIFT3 - PTE_FILE_SHIFT2 - 1)
+#define PTE_FILE_BITS3		(PTE_FILE_SHIFT4 - PTE_FILE_SHIFT3 - 1)
+
+#define pte_to_pgoff(pte)						\
+	((((pte).pte_low >> (PTE_FILE_SHIFT1))				\
+	  & ((1U << PTE_FILE_BITS1) - 1)))				\
+	+ ((((pte).pte_low >> (PTE_FILE_SHIFT2))			\
+	    & ((1U << PTE_FILE_BITS2) - 1))				\
+	   << (PTE_FILE_BITS1))						\
+	+ ((((pte).pte_low >> (PTE_FILE_SHIFT3))			\
+	    & ((1U << PTE_FILE_BITS3) - 1))				\
+	   << (PTE_FILE_BITS1 + PTE_FILE_BITS2))			\
+	+ ((((pte).pte_low >> (PTE_FILE_SHIFT4)))			\
+	    << (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3))
+
+#define pgoff_to_pte(off)						\
+	((pte_t) { .pte_low =						\
+	 ((((off)) & ((1U << PTE_FILE_BITS1) - 1)) << PTE_FILE_SHIFT1)	\
+	 + ((((off) >> PTE_FILE_BITS1)					\
+	     & ((1U << PTE_FILE_BITS2) - 1))				\
+	    << PTE_FILE_SHIFT2)						\
+	 + ((((off) >> (PTE_FILE_BITS1 + PTE_FILE_BITS2))		\
+	     & ((1U << PTE_FILE_BITS3) - 1))				\
+	    << PTE_FILE_SHIFT3)						\
+	 + ((((off) >>							\
+	      (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)))	\
+	    << PTE_FILE_SHIFT4)						\
+	 + _PAGE_FILE })
+
+#else /* CONFIG_MEM_SOFT_DIRTY */
+
 /*
  * Bits _PAGE_BIT_PRESENT, _PAGE_BIT_FILE and _PAGE_BIT_PROTNONE are taken,
- * split up the 29 bits of offset into this range:
+ * split up the 29 bits of offset into this range.
  */
 #define PTE_FILE_MAX_BITS	29
 #define PTE_FILE_SHIFT1		(_PAGE_BIT_PRESENT + 1)

@@ -88,6 +132,8 @@ static inline pmd_t native_pmdp_get_and_
 	    << PTE_FILE_SHIFT3)						\
 	 + _PAGE_FILE })
 
+#endif /* CONFIG_MEM_SOFT_DIRTY */
+
 /* Encode and de-code a swap entry */
 #if _PAGE_BIT_FILE < _PAGE_BIT_PROTNONE
 #define SWP_TYPE_BITS (_PAGE_BIT_FILE - _PAGE_BIT_PRESENT - 1)
arch/x86/include/asm/pgtable-3level.h +3 -0
Index: linux-2.6.git/arch/x86/include/asm/pgtable-3level.h
===================================================================
@@ -179,6 +179,9 @@ static inline pmd_t native_pmdp_get_and_
 /*
  * Bits 0, 6 and 7 are taken in the low part of the pte,
  * put the 32 bits of offset into the high part.
+ *
+ * For soft-dirty tracking 11 bit is taken from
+ * the low part of pte as well.
  */
 #define pte_to_pgoff(pte) ((pte).pte_high)
 #define pgoff_to_pte(off)						\
arch/x86/include/asm/pgtable.h +15 -0
Index: linux-2.6.git/arch/x86/include/asm/pgtable.h
===================================================================
@@ -329,6 +329,21 @@ static inline pte_t pte_swp_clear_soft_d
 	return pte_clear_flags(pte, _PAGE_SWP_SOFT_DIRTY);
 }
 
+static inline pte_t pte_file_clear_soft_dirty(pte_t pte)
+{
+	return pte_clear_flags(pte, _PAGE_SOFT_DIRTY);
+}
+
+static inline pte_t pte_file_mksoft_dirty(pte_t pte)
+{
+	return pte_set_flags(pte, _PAGE_SOFT_DIRTY);
+}
+
+static inline int pte_file_soft_dirty(pte_t pte)
+{
+	return pte_flags(pte) & _PAGE_SOFT_DIRTY;
+}
+
 /*
  * Mask out unsupported bits in a present pgprot.  Non-present pgprots
  * can use those bits for other purposes, so leave them be.
arch/x86/include/asm/pgtable_types.h +3 -1
Index: linux-2.6.git/arch/x86/include/asm/pgtable_types.h
===================================================================
@@ -61,8 +61,10 @@
  * they do not conflict with each other.
  */
 
+#define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_HIDDEN
+
 #ifdef CONFIG_MEM_SOFT_DIRTY
-#define _PAGE_SOFT_DIRTY	(_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN)
+#define _PAGE_SOFT_DIRTY	(_AT(pteval_t, 1) << _PAGE_BIT_SOFT_DIRTY)
 #else
 #define _PAGE_SOFT_DIRTY	(_AT(pteval_t, 0))
 #endif
fs/proc/task_mmu.c +2 -0
Index: linux-2.6.git/fs/proc/task_mmu.c
===================================================================
@@ -736,6 +736,8 @@ static inline void clear_soft_dirty(stru
 		ptent = pte_clear_flags(ptent, _PAGE_SOFT_DIRTY);
 	} else if (pte_swp_soft_dirty(ptent)) {
 		ptent = pte_swp_clear_soft_dirty(ptent);
+	} else if (pte_file(ptent)) {
+		ptent = pte_file_clear_soft_dirty(ptent);
 	}
 
 	set_pte_at(vma->vm_mm, addr, pte, ptent);
mm/fremap.c +11 -3
Index: linux-2.6.git/mm/fremap.c
===================================================================
@@ -57,17 +57,25 @@ static int install_file_pte(struct mm_st
 		unsigned long addr, unsigned long pgoff, pgprot_t prot)
 {
 	int err = -ENOMEM;
-	pte_t *pte;
+	pte_t *pte, ptfile;
 	spinlock_t *ptl;
 
 	pte = get_locked_pte(mm, addr, &ptl);
 	if (!pte)
 		goto out;
 
-	if (!pte_none(*pte))
+	ptfile = pgoff_to_pte(pgoff);
+
+	if (!pte_none(*pte)) {
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pte_present(*pte) &&
+		    pte_soft_dirty(*pte))
+			pte_file_mksoft_dirty(ptfile);
+#endif
 		zap_pte(mm, vma, addr, pte);
+	}
 
-	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
+	set_pte_at(mm, addr, pte, ptfile);
 	/*
 	 * We don't need to run update_mmu_cache() here because the "file pte"
 	 * being installed by install_file_pte() is not a real pte - it's a
mm/memory.c +16 -4
Index: linux-2.6.git/mm/memory.c
===================================================================
@@ -1141,9 +1141,14 @@ again:
 				continue;
 			if (unlikely(details) && details->nonlinear_vma
 			    && linear_page_index(details->nonlinear_vma,
-						addr) != page->index)
-				set_pte_at(mm, addr, pte,
-					   pgoff_to_pte(page->index));
+						addr) != page->index) {
+				pte_t ptfile = pgoff_to_pte(page->index);
+#ifdef CONFIG_MEM_SOFT_DIRTY
+				if (pte_soft_dirty(ptent))
+					pte_file_mksoft_dirty(ptfile);
+#endif
+				set_pte_at(mm, addr, pte, ptfile);
+			}
 			if (PageAnon(page))
 				rss[MM_ANONPAGES]--;
 			else {

@@ -3410,8 +3415,15 @@ static int __do_fault(struct mm_struct *
 	if (likely(pte_same(*page_table, orig_pte))) {
 		flush_icache_page(vma, page);
 		entry = mk_pte(page, vma->vm_page_prot);
-		if (flags & FAULT_FLAG_WRITE)
+		if (flags & FAULT_FLAG_WRITE) {
 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		}
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		else if (pte_file(orig_pte) &&
+			 pte_file_soft_dirty(orig_pte)) {
+			pte_mksoft_dirty(entry);
+		}
+#endif
 		if (anon) {
 			inc_mm_counter_fast(mm, MM_ANONPAGES);
 			page_add_new_anon_rmap(page, vma, address);
mm/rmap.c +8 -2
Index: linux-2.6.git/mm/rmap.c
===================================================================
@@ -1407,8 +1407,14 @@ static int try_to_unmap_cluster(unsigned
 		pteval = ptep_clear_flush(vma, address, pte);
 
 		/* If nonlinear, store the file page offset in the pte. */
-		if (page->index != linear_page_index(vma, address))
-			set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
+		if (page->index != linear_page_index(vma, address)) {
+			pte_t ptfile = pgoff_to_pte(page->index);
+#ifdef CONFIG_MEM_SOFT_DIRTY
+			if (pte_soft_dirty(pteval))
+				pte_file_mksoft_dirty(ptfile);
+#endif
+			set_pte_at(mm, address, pte, ptfile);
+		}
 
 		/* Move the dirty bit to the physical page now the pte is gone. */
 		if (pte_dirty(pteval))

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#1 lore raw
Quoted 5 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd (or whatever the next level is called) gets zapped? (Also, what happens if you unmap a file and map a different file there?)

--Andy

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

author
#2 lore raw
Quoted 9 lines · Andy Lutomirski
Quoted 5 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd

It's the same as encoding pgoff in pte entry (pte is not present), but together with pgoff we save soft-bit status, later on #pf we decode pgoff and restore softbit back if it was there, pte itself can't disappear since it holds pgoff information.

Quoted 2 lines

(or whatever the next level is called) gets zapped? (Also, what happens if you unmap a file and map a different file there?)

If file pages are remapped to a new place we remember softdity bit status previously has and propagate it to a new pte (as in install_file_pte, old ptes are cleared).

If file unmapped then new one mapped, pmd/ptes are cleared (including softbit) and it remains clear until new write happens, if only i've not missed something obvious.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#3 lore raw
Quoted 8 lines · Cyrill Gorcunov
Quoted 7 lines · Andy Lutomirski
Quoted 5 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Quoted 7 lines
Quoted 2 lines

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd

It's the same as encoding pgoff in pte entry (pte is not present), but together with pgoff we save soft-bit status, later on #pf we decode pgoff and restore softbit back if it was there, pte itself can't disappear since it holds pgoff information.

Isn't that only the case for nonlinear mappings?

--Andy

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

author
#4 lore raw
Quoted 9 lines · Andy Lutomirski
Quoted 7 lines
Quoted 2 lines

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd

It's the same as encoding pgoff in pte entry (pte is not present), but together with pgoff we save soft-bit status, later on #pf we decode pgoff and restore softbit back if it was there, pte itself can't disappear since it holds pgoff information.

Isn't that only the case for nonlinear mappings?

Andy, I'm somehow lost, pte either exist with file encoded, either not, when pud/ptes are zapped and any access to it should cause #pf pointing kernel to read/write data from file to a page, if it happens on write the pte is obtaining dirty bit (which always set together with soft bit).

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#5 lore raw
Quoted 9 lines · Cyrill Gorcunov
Quoted 8 lines · Andy Lutomirski
Quoted 7 lines
Quoted 2 lines

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd

It's the same as encoding pgoff in pte entry (pte is not present), but together with pgoff we save soft-bit status, later on #pf we decode pgoff and restore softbit back if it was there, pte itself can't disappear since it holds pgoff information.

Quoted 7 lines
Quoted 1 line

Isn't that only the case for nonlinear mappings?

Andy, I'm somehow lost, pte either exist with file encoded, either not, when pud/ptes are zapped and any access to it should cause #pf pointing kernel to read/write data from file to a page, if it happens on write the pte is obtaining dirty bit (which always set together with soft bit).

Hmm. I may have been wrong.

By my reading of this stuff, when a pte is freed to reclaim memory, if it's an un-cowed file mapping, it's cleared completely by zap_pte_range -- no swap entry is left behind. That's this code in zap_pte_range:

				/*
				 * unmap_shared_mapping_pages() wants to
				 * invalidate cache without truncating:
				 * unmap shared but keep private pages.
				 */
				if (details->check_mapping &&
				    details->check_mapping != page->mapping)
					continue;

In theory, if you map 2MB (on x86_64) of a file as MAP_PRIVATE, aligned, then you get a whole pmd. If you don't write any of it (triggering COW), the kernel could, in theory, free all those ptes, so you can't save any state in there. (I can't find any code that does this, though.)

That being said, a MAP_PRIVATE, un-cowed mapping must be clean -- if it had been (soft-)dirtied, it would also have been cowed. So you might be okay.

--Andy

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

author
#6 lore raw
Quoted 4 lines · Andy Lutomirski

That being said, a MAP_PRIVATE, un-cowed mapping must be clean -- if it had been (soft-)dirtied, it would also have been cowed. So you might be okay.

Yas, as far as I know we are either cow'ed or in clean state, thus either soft-bit set on #pf (and when reclaimed rest in file-pte) or it remains clean and there is no change we need to track.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#7 lore raw
In reply to Andy Lutomirski
Quoted 11 lines · Andy Lutomirski
Quoted 5 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd (or whatever the next level is called) gets zapped? (Also, what happens if you unmap a file and map a different file there?)

The whole pte gets zapped on vma unmap, and in this case forgetting the soft-dirty bit completely is OK.

Quoted 3 lines

--Andy
.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#8 lore raw
Quoted 8 lines · Pavel Emelyanov
Quoted 7 lines · Andy Lutomirski
Quoted 5 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Quoted 7 lines
Quoted 4 lines

Unless I'm misunderstanding this, it's saving the bit in the non-present PTE. This sounds wrong -- what happens if the entire pmd (or whatever the next level is called) gets zapped? (Also, what happens if you unmap a file and map a different file there?)

The whole pte gets zapped on vma unmap, and in this case forgetting the soft-dirty bit completely is OK.

I mean -- soft-dirty bits denote changes in the vm area, if you remove one, then it can be found out from the /proc/pid/maps file that the vma has disappeared.

But one problem really went unnoticed here -- if we map a new vma in place of some old one with the same flags and prots. It looks like we need a vma soft-dirty mark, that is set on mmap and mremap, is cleared on soft dirty clear and is propagated into pte pagemap bits.

Quoted 1 line
Quoted 1 line

--Andy

Thanks,
Pavel

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#9 lore raw
In reply to Cyrill Gorcunov
Quoted 25 lines · Cyrill Gorcunov

Andy reported that if file page get reclaimed we loose soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back.

Reported-by Andy Lutomirski <[email protected]>
Signed-off-by Cyrill Gorcunov <[email protected]>
Cc Pavel Emelyanov <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Matt Mackall <[email protected]>
Cc Xiao Guangrong <[email protected]>
Cc Marcelo Tosatti <[email protected]>
Cc KOSAKI Motohiro <[email protected]>
Cc Stephen Rothwell <[email protected]>

---

mm/fremap.c +1 -1
@@ -57,17 +57,25 @@ static int install_file_pte(struct mm_st
 		unsigned long addr, unsigned long pgoff, pgprot_t prot)
 {
 	int err = -ENOMEM;
-	pte_t *pte;
+	pte_t *pte, ptfile;
 	spinlock_t *ptl;
 
 	pte = get_locked_pte(mm, addr, &ptl);

mm/fremap.c static int install_file_pte(struct mm_st · line 72

Quoted 10 lines
mm/fremap.c +6 -1
 	if (!pte)
 		goto out;
 
-	if (!pte_none(*pte))
+	ptfile = pgoff_to_pte(pgoff);
+
+	if (!pte_none(*pte)) {
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pte_present(*pte) &&
+		    pte_soft_dirty(*pte))

I think there's no need in wrapping every such if () inside #ifdef CONFIG_..., since the pte_soft_dirty() routine itself would be 0 for non-soft-dirty case and compiler would optimize this code out.

mm/fremap.c static int install_file_pte(struct mm_st · line 81

Quoted 10 lines
mm/fremap.c +4 -1
+			pte_file_mksoft_dirty(ptfile);
+#endif
 		zap_pte(mm, vma, addr, pte);
+	}
 
-	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
+	set_pte_at(mm, addr, pte, ptfile);
 	/*
 	 * We don't need to run update_mmu_cache() here because the "file pte"
 	 * being installed by install_file_pte() is not a real pte - it's a

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

author
#10 lore raw
Quoted 12 lines · Pavel Emelyanov

mm/fremap.c static int install_file_pte(struct mm_st · line 72

Quoted 8 lines
mm/fremap.c +6 -1
-	if (!pte_none(*pte))
+	ptfile = pgoff_to_pte(pgoff);
+
+	if (!pte_none(*pte)) {
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pte_present(*pte) &&
+		    pte_soft_dirty(*pte))

I think there's no need in wrapping every such if () inside #ifdef CONFIG_..., since the pte_soft_dirty() routine itself would be 0 for non-soft-dirty case and compiler would optimize this code out.

If only I'm not missing something obvious, this code compiles not only on x86, CONFIG_MEM_SOFT_DIRTY depends on x86 (otherwise I'll have to implement pte_soft_dirty for all archs).

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#11 lore raw
Quoted 14 lines · Cyrill Gorcunov
Quoted 12 lines · Pavel Emelyanov

mm/fremap.c static int install_file_pte(struct mm_st · line 72

Quoted 8 lines
mm/fremap.c +6 -1
-	if (!pte_none(*pte))
+	ptfile = pgoff_to_pte(pgoff);
+
+	if (!pte_none(*pte)) {
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pte_present(*pte) &&
+		    pte_soft_dirty(*pte))

I think there's no need in wrapping every such if () inside #ifdef CONFIG_..., since the pte_soft_dirty() routine itself would be 0 for non-soft-dirty case and compiler would optimize this code out.

Quoted 3 lines

If only I'm not missing something obvious, this code compiles not only on x86, CONFIG_MEM_SOFT_DIRTY depends on x86 (otherwise I'll have to implement pte_soft_dirty for all archs).

For non-x86 case there are stubs in include/asm-generic/pgtable.h that would act as if the CONFIG_MEM_SOFT_DIRTY is off.

Thanks,
Pavel

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

#13 lore raw
In reply to Cyrill Gorcunov
Quoted 14 lines · Cyrill Gorcunov
Quoted 12 lines · Pavel Emelyanov

mm/fremap.c static int install_file_pte(struct mm_st · line 72

Quoted 8 lines
mm/fremap.c +6 -1
-	if (!pte_none(*pte))
+	ptfile = pgoff_to_pte(pgoff);
+
+	if (!pte_none(*pte)) {
+#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pte_present(*pte) &&
+		    pte_soft_dirty(*pte))

I think there's no need in wrapping every such if () inside #ifdef CONFIG_..., since the pte_soft_dirty() routine itself would be 0 for non-soft-dirty case and compiler would optimize this code out.

Quoted 3 lines

If only I'm not missing something obvious, this code compiles not only on x86, CONFIG_MEM_SOFT_DIRTY depends on x86 (otherwise I'll have to implement pte_soft_dirty for all archs).

why not

#ifndef pte_soft_dirty
#define pte_soft_dirty(pte) 0
#endif

and on x86
#define pte_soft_dirty pte_soft_dirty

-aneesh

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

author
#14 lore raw
Quoted 5 lines · Aneesh Kumar K.V
Quoted 4 lines

If only I'm not missing something obvious, this code compiles not only on x86, CONFIG_MEM_SOFT_DIRTY depends on x86 (otherwise I'll have to implement pte_soft_dirty for all archs).

Quoted 8 lines

why not

#ifndef pte_soft_dirty
#define pte_soft_dirty(pte) 0
#endif

and on x86
#define pte_soft_dirty pte_soft_dirty

Yeah, either this way, either to use asm-generic (later I think more preferred), thanks!

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>