| Message ID | 20240408042437.10951-3-ioworker0@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/madvise: enhance lazyfreeing with mTHP in madvise_free | expand |
On 08/04/2024 05:24, Lance Yang wrote: > The per-pte get_and_clear/modify/set approach would result in > unfolding/refolding for contpte mappings on arm64. So we need > to override mkold_clean_ptes() for arm64 to avoid it. IIRC, in the last version, I suggested copying the wrprotect_ptes() pattern to correctly iterate over contpte blocks. I meant for you to take it as inspiration but looks like you have done a carbon copy, including lots of things that are unneeded here. That's my fault for not being clear - sorry! > > Suggested-by: David Hildenbrand <david@redhat.com> > Suggested-by: Barry Song <21cnbao@gmail.com> > Suggested-by: Ryan Roberts <ryan.roberts@arm.com> > Signed-off-by: Lance Yang <ioworker0@gmail.com> > --- > arch/arm64/include/asm/pgtable.h | 55 ++++++++++++++++++++++++++++++++ > arch/arm64/mm/contpte.c | 15 +++++++++ > 2 files changed, 70 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 9fd8613b2db2..395754638a9a 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -1223,6 +1223,34 @@ static inline void __wrprotect_ptes(struct mm_struct *mm, unsigned long address, > __ptep_set_wrprotect(mm, address, ptep); > } > > +static inline void ___ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + pte_t old_pte; > + > + do { > + old_pte = pte; > + pte = pte_mkclean(pte_mkold(pte)); > + pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep), > + pte_val(old_pte), pte_val(pte)); > + } while (pte_val(pte) != pte_val(old_pte)); > +} Given you are clearing old and dirty, you have nothing to race against, so you shouldn't need the cmpxchg loop here; just a get/modify/set should do? Of course if you are setting one or the other, then you need the loop. > + > +static inline void __ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep) > +{ > + ___ptep_mkold_clean(mm, addr, ptep, __ptep_get(ptep)); > +} I don't see a need for this intermediate function. > + > +static inline void __mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, unsigned int nr) > +{ > + unsigned int i; > + > + for (i = 0; i < nr; i++, addr += PAGE_SIZE, ptep++) It would probably be good to use the for() loop pattern used by the generic impls here too. > + __ptep_mkold_clean(mm, addr, ptep); > +} > + > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > #define __HAVE_ARCH_PMDP_SET_WRPROTECT > static inline void pmdp_set_wrprotect(struct mm_struct *mm, > @@ -1379,6 +1407,8 @@ extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty); > +extern void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, unsigned int nr); > > static __always_inline void contpte_try_fold(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, pte_t pte) > @@ -1603,6 +1633,30 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty); > } > > +#define mkold_clean_ptes mkold_clean_ptes > +static inline void mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, unsigned int nr) > +{ > + if (likely(nr == 1)) { > + /* > + * Optimization: mkold_clean_ptes() can only be called for present > + * ptes so we only need to check contig bit as condition for unfold, > + * and we can remove the contig bit from the pte we read to avoid > + * re-reading. This speeds up madvise(MADV_FREE) which is sensitive > + * for order-0 folios. Equivalent to contpte_try_unfold(). > + */ Is this true? Do you have data that shows the cost? If not, I'd prefer to avoid the optimization and do it the more standard way: contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > + pte_t orig_pte = __ptep_get(ptep); > + > + if (unlikely(pte_cont(orig_pte))) { > + __contpte_try_unfold(mm, addr, ptep, orig_pte); > + orig_pte = pte_mknoncont(orig_pte); > + } > + ___ptep_mkold_clean(mm, addr, ptep, orig_pte); > + } else { > + contpte_mkold_clean_ptes(mm, addr, ptep, nr); > + } ...but I don't think you should ever need to unfold in the first place. Even if it's folded and you are trying to clear access/dirty for a single pte, you can just clear the whole block. See existing comment in contpte_ptep_test_and_clear_young(). So this ends up as something like: static inline void clear_young_dirty_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep, unsigned int nr, bool clear_young, bool clear_dirty) { if (likely(nr == 1 && !pte_cont(__ptep_get(ptep)))) clear_young_dirty_ptes(mm, addr, ptep, nr, clear_young, clear_dirty); else contpte_clear_young_dirty_ptes(mm, addr, ptep, nr, clear_young, clear_dirty); } > +} > + > #else /* CONFIG_ARM64_CONTPTE */ > > #define ptep_get __ptep_get > @@ -1622,6 +1676,7 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > #define wrprotect_ptes __wrprotect_ptes > #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS > #define ptep_set_access_flags __ptep_set_access_flags > +#define mkold_clean_ptes __mkold_clean_ptes > > #endif /* CONFIG_ARM64_CONTPTE */ > > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 1b64b4c3f8bf..dbff9c5e9eff 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -361,6 +361,21 @@ void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > } > EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes); > > +void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, unsigned int nr) > +{ > + /* > + * If clearing the young and dirty bits for an entire contig range, we can > + * avoid unfolding. Just set old/clean and wait for the later mmu_gather > + * flush to invalidate the tlb. If it's a partial range though, we need to > + * unfold. > + */ nit: Please reflow comments like this to 80 cols. We can avoid unfolding in all cases. See existing comment in contpte_ptep_test_and_clear_young(). Suggest something like this (untested): void clear_young_dirty_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep, unsigned int nr, bool clear_young, bool clear_dirty) { /* * We can safely clear access/dirty without needing to unfold from the * architectures perspective, even when contpte is set. If the range * starts or ends midway through a contpte block, we can just expand to * include the full contpte block. While this is not exactly what the * core-mm asked for, it tracks access/dirty per folio, not per page. * And since we only create a contpte block when it is covered by a * single folio, we can get away with clearing access/dirty for the * whole block. */ unsigned int start = addr; unsigned int end = start + nr; if (pte_cont(__ptep_get(ptep + nr - 1))) end = ALIGN(end, CONT_PTE_SIZE); if (pte_cont(__ptep_get(ptep))) { start = ALIGN_DOWN(start, CONT_PTE_SIZE); ptep = contpte_align_down(ptep); } __clear_young_dirty_ptes(mm, start, ptep, end - start, clear_young, clear_dirty); } Thanks, Ryan > + > + contpte_try_unfold_partial(mm, addr, ptep, nr); > + __mkold_clean_ptes(mm, addr, ptep, nr); > +} > +EXPORT_SYMBOL_GPL(contpte_mkold_clean_ptes); > + > int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty)
On Thu, Apr 11, 2024 at 9:17 PM Ryan Roberts <ryan.roberts@arm.com> wrote: > > On 08/04/2024 05:24, Lance Yang wrote: > > The per-pte get_and_clear/modify/set approach would result in > > unfolding/refolding for contpte mappings on arm64. So we need > > to override mkold_clean_ptes() for arm64 to avoid it. > > IIRC, in the last version, I suggested copying the wrprotect_ptes() pattern to > correctly iterate over contpte blocks. I meant for you to take it as inspiration > but looks like you have done a carbon copy, including lots of things that are > unneeded here. That's my fault for not being clear - sorry! My bad. I must have misunderstood your intention. > > > > > > Suggested-by: David Hildenbrand <david@redhat.com> > > Suggested-by: Barry Song <21cnbao@gmail.com> > > Suggested-by: Ryan Roberts <ryan.roberts@arm.com> > > Signed-off-by: Lance Yang <ioworker0@gmail.com> > > --- > > arch/arm64/include/asm/pgtable.h | 55 ++++++++++++++++++++++++++++++++ > > arch/arm64/mm/contpte.c | 15 +++++++++ > > 2 files changed, 70 insertions(+) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index 9fd8613b2db2..395754638a9a 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -1223,6 +1223,34 @@ static inline void __wrprotect_ptes(struct mm_struct *mm, unsigned long address, > > __ptep_set_wrprotect(mm, address, ptep); > > } > > > > +static inline void ___ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep, pte_t pte) > > +{ > > + pte_t old_pte; > > + > > + do { > > + old_pte = pte; > > + pte = pte_mkclean(pte_mkold(pte)); > > + pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep), > > + pte_val(old_pte), pte_val(pte)); > > + } while (pte_val(pte) != pte_val(old_pte)); > > +} > > Given you are clearing old and dirty, you have nothing to race against, so you > shouldn't need the cmpxchg loop here; just a get/modify/set should do? Of course > if you are setting one or the other, then you need the loop. Got it. > > > + > > +static inline void __ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep) > > +{ > > + ___ptep_mkold_clean(mm, addr, ptep, __ptep_get(ptep)); > > +} > > I don't see a need for this intermediate function. > > > + > > +static inline void __mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep, unsigned int nr) > > +{ > > + unsigned int i; > > + > > + for (i = 0; i < nr; i++, addr += PAGE_SIZE, ptep++) > > It would probably be good to use the for() loop pattern used by the generic > impls here too. Got it. > > > + __ptep_mkold_clean(mm, addr, ptep); > > +} > > + > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > #define __HAVE_ARCH_PMDP_SET_WRPROTECT > > static inline void pmdp_set_wrprotect(struct mm_struct *mm, > > @@ -1379,6 +1407,8 @@ extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > > extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > > unsigned long addr, pte_t *ptep, > > pte_t entry, int dirty); > > +extern void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep, unsigned int nr); > > > > static __always_inline void contpte_try_fold(struct mm_struct *mm, > > unsigned long addr, pte_t *ptep, pte_t pte) > > @@ -1603,6 +1633,30 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > > return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty); > > } > > > > +#define mkold_clean_ptes mkold_clean_ptes > > +static inline void mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep, unsigned int nr) > > +{ > > + if (likely(nr == 1)) { > > + /* > > + * Optimization: mkold_clean_ptes() can only be called for present > > + * ptes so we only need to check contig bit as condition for unfold, > > + * and we can remove the contig bit from the pte we read to avoid > > + * re-reading. This speeds up madvise(MADV_FREE) which is sensitive > > + * for order-0 folios. Equivalent to contpte_try_unfold(). > > + */ > > Is this true? Do you have data that shows the cost? If not, I'd prefer to avoid > the optimization and do it the more standard way: > > contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > > > + pte_t orig_pte = __ptep_get(ptep); > > + > > + if (unlikely(pte_cont(orig_pte))) { > > + __contpte_try_unfold(mm, addr, ptep, orig_pte); > > + orig_pte = pte_mknoncont(orig_pte); > > + } > > + ___ptep_mkold_clean(mm, addr, ptep, orig_pte); > > + } else { > > + contpte_mkold_clean_ptes(mm, addr, ptep, nr); > > + } > > ...but I don't think you should ever need to unfold in the first place. Even if > it's folded and you are trying to clear access/dirty for a single pte, you can > just clear the whole block. See existing comment in > contpte_ptep_test_and_clear_young(). Thanks for pointing that out. > > So this ends up as something like: > > static inline void clear_young_dirty_ptes(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, unsigned int nr, > bool clear_young, bool clear_dirty) > { > if (likely(nr == 1 && !pte_cont(__ptep_get(ptep)))) > clear_young_dirty_ptes(mm, addr, ptep, nr, > clear_young, clear_dirty); > else > contpte_clear_young_dirty_ptes(mm, addr, ptep, nr, > clear_young, clear_dirty); > } Nice. I'll make sure to follow this approach. > > > > +} > > + > > #else /* CONFIG_ARM64_CONTPTE */ > > > > #define ptep_get __ptep_get > > @@ -1622,6 +1676,7 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > > #define wrprotect_ptes __wrprotect_ptes > > #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS > > #define ptep_set_access_flags __ptep_set_access_flags > > +#define mkold_clean_ptes __mkold_clean_ptes > > > > #endif /* CONFIG_ARM64_CONTPTE */ > > > > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > > index 1b64b4c3f8bf..dbff9c5e9eff 100644 > > --- a/arch/arm64/mm/contpte.c > > +++ b/arch/arm64/mm/contpte.c > > @@ -361,6 +361,21 @@ void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, > > } > > EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes); > > > > +void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, > > + pte_t *ptep, unsigned int nr) > > +{ > > + /* > > + * If clearing the young and dirty bits for an entire contig range, we can > > + * avoid unfolding. Just set old/clean and wait for the later mmu_gather > > + * flush to invalidate the tlb. If it's a partial range though, we need to > > + * unfold. > > + */ > > nit: Please reflow comments like this to 80 cols. > > We can avoid unfolding in all cases. See existing comment in > contpte_ptep_test_and_clear_young(). Suggest something like this (untested): > > void clear_young_dirty_ptes(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, unsigned int nr, > bool clear_young, bool clear_dirty) > { > /* > * We can safely clear access/dirty without needing to unfold from the > * architectures perspective, even when contpte is set. If the range > * starts or ends midway through a contpte block, we can just expand to > * include the full contpte block. While this is not exactly what the > * core-mm asked for, it tracks access/dirty per folio, not per page. > * And since we only create a contpte block when it is covered by a > * single folio, we can get away with clearing access/dirty for the > * whole block. > */ > > unsigned int start = addr; > unsigned int end = start + nr; > > if (pte_cont(__ptep_get(ptep + nr - 1))) > end = ALIGN(end, CONT_PTE_SIZE); > > if (pte_cont(__ptep_get(ptep))) { > start = ALIGN_DOWN(start, CONT_PTE_SIZE); > ptep = contpte_align_down(ptep); > } > > __clear_young_dirty_ptes(mm, start, ptep, end - start, > clear_young, clear_dirty); > } Nice. Thanks a lot for your help! Thanks, Lance > > Thanks, > Ryan > > > + > > + contpte_try_unfold_partial(mm, addr, ptep, nr); > > + __mkold_clean_ptes(mm, addr, ptep, nr); > > +} > > +EXPORT_SYMBOL_GPL(contpte_mkold_clean_ptes); > > + > > int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > > unsigned long addr, pte_t *ptep, > > pte_t entry, int dirty) >
On 12/04/2024 03:09, Lance Yang wrote: > On Thu, Apr 11, 2024 at 9:17 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >> >> On 08/04/2024 05:24, Lance Yang wrote: >>> The per-pte get_and_clear/modify/set approach would result in >>> unfolding/refolding for contpte mappings on arm64. So we need >>> to override mkold_clean_ptes() for arm64 to avoid it. >> >> IIRC, in the last version, I suggested copying the wrprotect_ptes() pattern to >> correctly iterate over contpte blocks. I meant for you to take it as inspiration >> but looks like you have done a carbon copy, including lots of things that are >> unneeded here. That's my fault for not being clear - sorry! > > My bad. I must have misunderstood your intention. Not at all - it was my bad. wrprotect_ptes() is nothing like what I eventually suggested below, so sorry for the bad steer.
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 9fd8613b2db2..395754638a9a 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1223,6 +1223,34 @@ static inline void __wrprotect_ptes(struct mm_struct *mm, unsigned long address, __ptep_set_wrprotect(mm, address, ptep); } +static inline void ___ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte) +{ + pte_t old_pte; + + do { + old_pte = pte; + pte = pte_mkclean(pte_mkold(pte)); + pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep), + pte_val(old_pte), pte_val(pte)); + } while (pte_val(pte) != pte_val(old_pte)); +} + +static inline void __ptep_mkold_clean(struct mm_struct *mm, unsigned long addr, + pte_t *ptep) +{ + ___ptep_mkold_clean(mm, addr, ptep, __ptep_get(ptep)); +} + +static inline void __mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, unsigned int nr) +{ + unsigned int i; + + for (i = 0; i < nr; i++, addr += PAGE_SIZE, ptep++) + __ptep_mkold_clean(mm, addr, ptep); +} + #ifdef CONFIG_TRANSPARENT_HUGEPAGE #define __HAVE_ARCH_PMDP_SET_WRPROTECT static inline void pmdp_set_wrprotect(struct mm_struct *mm, @@ -1379,6 +1407,8 @@ extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t entry, int dirty); +extern void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, unsigned int nr); static __always_inline void contpte_try_fold(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte) @@ -1603,6 +1633,30 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty); } +#define mkold_clean_ptes mkold_clean_ptes +static inline void mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, unsigned int nr) +{ + if (likely(nr == 1)) { + /* + * Optimization: mkold_clean_ptes() can only be called for present + * ptes so we only need to check contig bit as condition for unfold, + * and we can remove the contig bit from the pte we read to avoid + * re-reading. This speeds up madvise(MADV_FREE) which is sensitive + * for order-0 folios. Equivalent to contpte_try_unfold(). + */ + pte_t orig_pte = __ptep_get(ptep); + + if (unlikely(pte_cont(orig_pte))) { + __contpte_try_unfold(mm, addr, ptep, orig_pte); + orig_pte = pte_mknoncont(orig_pte); + } + ___ptep_mkold_clean(mm, addr, ptep, orig_pte); + } else { + contpte_mkold_clean_ptes(mm, addr, ptep, nr); + } +} + #else /* CONFIG_ARM64_CONTPTE */ #define ptep_get __ptep_get @@ -1622,6 +1676,7 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, #define wrprotect_ptes __wrprotect_ptes #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS #define ptep_set_access_flags __ptep_set_access_flags +#define mkold_clean_ptes __mkold_clean_ptes #endif /* CONFIG_ARM64_CONTPTE */ diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c index 1b64b4c3f8bf..dbff9c5e9eff 100644 --- a/arch/arm64/mm/contpte.c +++ b/arch/arm64/mm/contpte.c @@ -361,6 +361,21 @@ void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, } EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes); +void contpte_mkold_clean_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, unsigned int nr) +{ + /* + * If clearing the young and dirty bits for an entire contig range, we can + * avoid unfolding. Just set old/clean and wait for the later mmu_gather + * flush to invalidate the tlb. If it's a partial range though, we need to + * unfold. + */ + + contpte_try_unfold_partial(mm, addr, ptep, nr); + __mkold_clean_ptes(mm, addr, ptep, nr); +} +EXPORT_SYMBOL_GPL(contpte_mkold_clean_ptes); + int contpte_ptep_set_access_flags(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t entry, int dirty)
The per-pte get_and_clear/modify/set approach would result in unfolding/refolding for contpte mappings on arm64. So we need to override mkold_clean_ptes() for arm64 to avoid it. Suggested-by: David Hildenbrand <david@redhat.com> Suggested-by: Barry Song <21cnbao@gmail.com> Suggested-by: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Lance Yang <ioworker0@gmail.com> --- arch/arm64/include/asm/pgtable.h | 55 ++++++++++++++++++++++++++++++++ arch/arm64/mm/contpte.c | 15 +++++++++ 2 files changed, 70 insertions(+)