| Message ID | 20250113033901.68951-5-21cnbao@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | mm: batched unmap lazyfree large folios during reclamation | expand |
On 2025/1/13 11:39, Barry Song wrote: > From: Barry Song <v-songbaohua@oppo.com> > > The try_to_unmap_one() function currently handles PMD-mapped THPs > inefficiently. It first splits the PMD into PTEs, copies the dirty > state from the PMD to the PTEs, iterates over the PTEs to locate > the dirty state, and then marks the THP as swap-backed. This process > involves unnecessary PMD splitting and redundant iteration. Instead, > this functionality can be efficiently managed in > __discard_anon_folio_pmd_locked(), avoiding the extra steps and > improving performance. > > The following microbenchmark redirties folios after invoking MADV_FREE, > then measures the time taken to perform memory reclamation (actually > set those folios swapbacked again) on the redirtied folios. > > #include <stdio.h> > #include <sys/mman.h> > #include <string.h> > #include <time.h> > > #define SIZE 128*1024*1024 // 128 MB > > int main(int argc, char *argv[]) > { > while(1) { > volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > memset((void *)p, 1, SIZE); > madvise((void *)p, SIZE, MADV_FREE); > /* redirty after MADV_FREE */ > memset((void *)p, 1, SIZE); > > clock_t start_time = clock(); > madvise((void *)p, SIZE, MADV_PAGEOUT); > clock_t end_time = clock(); > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > printf("Time taken by reclamation: %f seconds\n", elapsed_time); > > munmap((void *)p, SIZE); > } > return 0; > } > > Testing results are as below, > w/o patch: > ~ # ./a.out > Time taken by reclamation: 0.007300 seconds > Time taken by reclamation: 0.007226 seconds > Time taken by reclamation: 0.007295 seconds > Time taken by reclamation: 0.007731 seconds > Time taken by reclamation: 0.007134 seconds > Time taken by reclamation: 0.007285 seconds > Time taken by reclamation: 0.007720 seconds > Time taken by reclamation: 0.007128 seconds > Time taken by reclamation: 0.007710 seconds > Time taken by reclamation: 0.007712 seconds > Time taken by reclamation: 0.007236 seconds > Time taken by reclamation: 0.007690 seconds > Time taken by reclamation: 0.007174 seconds > Time taken by reclamation: 0.007670 seconds > Time taken by reclamation: 0.007169 seconds > Time taken by reclamation: 0.007305 seconds > Time taken by reclamation: 0.007432 seconds > Time taken by reclamation: 0.007158 seconds > Time taken by reclamation: 0.007133 seconds > … > > w/ patch > > ~ # ./a.out > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002116 seconds > Time taken by reclamation: 0.002150 seconds > Time taken by reclamation: 0.002261 seconds > Time taken by reclamation: 0.002137 seconds > Time taken by reclamation: 0.002173 seconds > Time taken by reclamation: 0.002063 seconds > Time taken by reclamation: 0.002088 seconds > Time taken by reclamation: 0.002169 seconds > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002111 seconds > Time taken by reclamation: 0.002224 seconds > Time taken by reclamation: 0.002297 seconds > Time taken by reclamation: 0.002260 seconds > Time taken by reclamation: 0.002246 seconds > Time taken by reclamation: 0.002272 seconds > Time taken by reclamation: 0.002277 seconds > Time taken by reclamation: 0.002462 seconds > … > > This patch significantly speeds up try_to_unmap_one() by allowing it > to skip redirtied THPs without splitting the PMD. > > Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com> > Suggested-by: Lance Yang <ioworker0@gmail.com> > Signed-off-by: Barry Song <v-songbaohua@oppo.com> > --- > mm/huge_memory.c | 17 ++++++++++++++--- > mm/rmap.c | 11 ++++++++++- > 2 files changed, 24 insertions(+), 4 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 3d3ebdc002d5..aea49f7125f1 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > int ref_count, map_count; > pmd_t orig_pmd = *pmdp; > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > + if (pmd_dirty(orig_pmd)) > + folio_set_dirty(folio); > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > + folio_set_swapbacked(folio); > return false; > + } > > orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > > @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > * > * The only folio refs must be one from isolation plus the rmap(s). > */ > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > - ref_count != map_count + 1) { > + if (pmd_dirty(orig_pmd)) > + folio_set_dirty(folio); > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > + folio_set_swapbacked(folio); > + set_pmd_at(mm, addr, pmdp, orig_pmd); > + return false; > + } > + > + if (ref_count != map_count + 1) { > set_pmd_at(mm, addr, pmdp, orig_pmd); > return false; > } > diff --git a/mm/rmap.c b/mm/rmap.c > index 3ef659310797..02c4e4b2cd7b 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > pte_t pteval; > struct page *subpage; > - bool anon_exclusive, ret = true; > + bool anon_exclusive, lazyfree, ret = true; > struct mmu_notifier_range range; > enum ttu_flags flags = (enum ttu_flags)(long)arg; > int nr_pages = 1; > @@ -1724,9 +1724,18 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte) { > + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); You've checked lazyfree here, so can we remove the duplicate check in unmap_huge_pmd_locked()? Then the code should be: if (lazyfree && unmap_huge_pmd_locked(...)) goto walk_done; > if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > folio)) > goto walk_done; > + /* > + * unmap_huge_pmd_locked has either already marked > + * the folio as swap-backed or decided to retain it > + * due to GUP or speculative references. > + */ > + if (lazyfree) > + goto walk_abort; > > if (flags & TTU_SPLIT_HUGE_PMD) { > /*
On Tue, Jan 14, 2025 at 4:40 PM Baolin Wang <baolin.wang@linux.alibaba.com> wrote: > > > > On 2025/1/13 11:39, Barry Song wrote: > > From: Barry Song <v-songbaohua@oppo.com> > > > > The try_to_unmap_one() function currently handles PMD-mapped THPs > > inefficiently. It first splits the PMD into PTEs, copies the dirty > > state from the PMD to the PTEs, iterates over the PTEs to locate > > the dirty state, and then marks the THP as swap-backed. This process > > involves unnecessary PMD splitting and redundant iteration. Instead, > > this functionality can be efficiently managed in > > __discard_anon_folio_pmd_locked(), avoiding the extra steps and > > improving performance. > > > > The following microbenchmark redirties folios after invoking MADV_FREE, > > then measures the time taken to perform memory reclamation (actually > > set those folios swapbacked again) on the redirtied folios. > > > > #include <stdio.h> > > #include <sys/mman.h> > > #include <string.h> > > #include <time.h> > > > > #define SIZE 128*1024*1024 // 128 MB > > > > int main(int argc, char *argv[]) > > { > > while(1) { > > volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, > > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > > > memset((void *)p, 1, SIZE); > > madvise((void *)p, SIZE, MADV_FREE); > > /* redirty after MADV_FREE */ > > memset((void *)p, 1, SIZE); > > > > clock_t start_time = clock(); > > madvise((void *)p, SIZE, MADV_PAGEOUT); > > clock_t end_time = clock(); > > > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > > printf("Time taken by reclamation: %f seconds\n", elapsed_time); > > > > munmap((void *)p, SIZE); > > } > > return 0; > > } > > > > Testing results are as below, > > w/o patch: > > ~ # ./a.out > > Time taken by reclamation: 0.007300 seconds > > Time taken by reclamation: 0.007226 seconds > > Time taken by reclamation: 0.007295 seconds > > Time taken by reclamation: 0.007731 seconds > > Time taken by reclamation: 0.007134 seconds > > Time taken by reclamation: 0.007285 seconds > > Time taken by reclamation: 0.007720 seconds > > Time taken by reclamation: 0.007128 seconds > > Time taken by reclamation: 0.007710 seconds > > Time taken by reclamation: 0.007712 seconds > > Time taken by reclamation: 0.007236 seconds > > Time taken by reclamation: 0.007690 seconds > > Time taken by reclamation: 0.007174 seconds > > Time taken by reclamation: 0.007670 seconds > > Time taken by reclamation: 0.007169 seconds > > Time taken by reclamation: 0.007305 seconds > > Time taken by reclamation: 0.007432 seconds > > Time taken by reclamation: 0.007158 seconds > > Time taken by reclamation: 0.007133 seconds > > … > > > > w/ patch > > > > ~ # ./a.out > > Time taken by reclamation: 0.002124 seconds > > Time taken by reclamation: 0.002116 seconds > > Time taken by reclamation: 0.002150 seconds > > Time taken by reclamation: 0.002261 seconds > > Time taken by reclamation: 0.002137 seconds > > Time taken by reclamation: 0.002173 seconds > > Time taken by reclamation: 0.002063 seconds > > Time taken by reclamation: 0.002088 seconds > > Time taken by reclamation: 0.002169 seconds > > Time taken by reclamation: 0.002124 seconds > > Time taken by reclamation: 0.002111 seconds > > Time taken by reclamation: 0.002224 seconds > > Time taken by reclamation: 0.002297 seconds > > Time taken by reclamation: 0.002260 seconds > > Time taken by reclamation: 0.002246 seconds > > Time taken by reclamation: 0.002272 seconds > > Time taken by reclamation: 0.002277 seconds > > Time taken by reclamation: 0.002462 seconds > > … > > > > This patch significantly speeds up try_to_unmap_one() by allowing it > > to skip redirtied THPs without splitting the PMD. > > > > Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com> > > Suggested-by: Lance Yang <ioworker0@gmail.com> > > Signed-off-by: Barry Song <v-songbaohua@oppo.com> > > --- > > mm/huge_memory.c | 17 ++++++++++++++--- > > mm/rmap.c | 11 ++++++++++- > > 2 files changed, 24 insertions(+), 4 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 3d3ebdc002d5..aea49f7125f1 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > > int ref_count, map_count; > > pmd_t orig_pmd = *pmdp; > > > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > > + if (pmd_dirty(orig_pmd)) > > + folio_set_dirty(folio); > > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > > + folio_set_swapbacked(folio); > > return false; > > + } > > > > orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > > > > @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > > * > > * The only folio refs must be one from isolation plus the rmap(s). > > */ > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > > - ref_count != map_count + 1) { > > + if (pmd_dirty(orig_pmd)) > > + folio_set_dirty(folio); > > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > > + folio_set_swapbacked(folio); > > + set_pmd_at(mm, addr, pmdp, orig_pmd); > > + return false; > > + } > > + > > + if (ref_count != map_count + 1) { > > set_pmd_at(mm, addr, pmdp, orig_pmd); > > return false; > > } > > diff --git a/mm/rmap.c b/mm/rmap.c > > index 3ef659310797..02c4e4b2cd7b 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > > pte_t pteval; > > struct page *subpage; > > - bool anon_exclusive, ret = true; > > + bool anon_exclusive, lazyfree, ret = true; > > struct mmu_notifier_range range; > > enum ttu_flags flags = (enum ttu_flags)(long)arg; > > int nr_pages = 1; > > @@ -1724,9 +1724,18 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > } > > > > if (!pvmw.pte) { > > + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); > > You've checked lazyfree here, so can we remove the duplicate check in > unmap_huge_pmd_locked()? Then the code should be: > > if (lazyfree && unmap_huge_pmd_locked(...)) > goto walk_done; right. it seems unmap_huge_pmd_locked() only handles lazyfree pmd-mapped thp. so i guess the code could be: diff --git a/mm/huge_memory.c b/mm/huge_memory.c index aea49f7125f1..c4c3a7896de4 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3131,11 +3131,10 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); - - return false; + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); } static void remap_page(struct folio *folio, unsigned long nr, int flags) diff --git a/mm/rmap.c b/mm/rmap.c index 02c4e4b2cd7b..72907eb1b8fe 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); pte_t pteval; struct page *subpage; - bool anon_exclusive, lazyfree, ret = true; + bool anon_exclusive, ret = true; struct mmu_notifier_range range; enum ttu_flags flags = (enum ttu_flags)(long)arg; int nr_pages = 1; @@ -1724,18 +1724,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, } if (!pvmw.pte) { - lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); - - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, - folio)) - goto walk_done; - /* - * unmap_huge_pmd_locked has either already marked - * the folio as swap-backed or decided to retain it - * due to GUP or speculative references. - */ - if (lazyfree) + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) + goto walk_done; + /* + * unmap_huge_pmd_locked has either already marked + * the folio as swap-backed or decided to retain it + * due to GUP or speculative references. + */ goto walk_abort; + } if (flags & TTU_SPLIT_HUGE_PMD) { /* > > > if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > > folio)) > > goto walk_done; > > + /* > > + * unmap_huge_pmd_locked has either already marked > > + * the folio as swap-backed or decided to retain it > > + * due to GUP or speculative references. > > + */ > > + if (lazyfree) > > + goto walk_abort; > > > > if (flags & TTU_SPLIT_HUGE_PMD) { > > /*
> > > if (!pvmw.pte) { > > > + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); > > > > You've checked lazyfree here, so can we remove the duplicate check in > > unmap_huge_pmd_locked()? Then the code should be: > > > > if (lazyfree && unmap_huge_pmd_locked(...)) > > goto walk_done; > > > right. it seems unmap_huge_pmd_locked() only handles lazyfree pmd-mapped > thp. so i guess the code could be: > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index aea49f7125f1..c4c3a7896de4 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3131,11 +3131,10 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); > VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); > + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); > + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); > > - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > - > - return false; > + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > } > > static void remap_page(struct folio *folio, unsigned long nr, int flags) > diff --git a/mm/rmap.c b/mm/rmap.c > index 02c4e4b2cd7b..72907eb1b8fe 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > pte_t pteval; > struct page *subpage; > - bool anon_exclusive, lazyfree, ret = true; > + bool anon_exclusive, ret = true; > struct mmu_notifier_range range; > enum ttu_flags flags = (enum ttu_flags)(long)arg; > int nr_pages = 1; > @@ -1724,18 +1724,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte) { > - lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); > - > - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > - folio)) > - goto walk_done; > - /* > - * unmap_huge_pmd_locked has either already marked > - * the folio as swap-backed or decided to retain it > - * due to GUP or speculative references. > - */ > - if (lazyfree) > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { > + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) > + goto walk_done; > + /* > + * unmap_huge_pmd_locked has either already marked > + * the folio as swap-backed or decided to retain it > + * due to GUP or speculative references. > + */ > goto walk_abort; > + } > > if (flags & TTU_SPLIT_HUGE_PMD) { > /* > > > > > > if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > > > folio)) > > > goto walk_done; > > > + /* > > > + * unmap_huge_pmd_locked has either already marked > > > + * the folio as swap-backed or decided to retain it > > > + * due to GUP or speculative references. > > > + */ > > > + if (lazyfree) > > > + goto walk_abort; > > > > > > if (flags & TTU_SPLIT_HUGE_PMD) { > > > /* The final diff is as follows. Baolin, do you have any additional comments before I send out v3? diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 3d3ebdc002d5..47cc8c3f8f80 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, int ref_count, map_count; pmd_t orig_pmd = *pmdp; - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); return false; + } orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, * * The only folio refs must be one from isolation plus the rmap(s). */ - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || - ref_count != map_count + 1) { + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); + set_pmd_at(mm, addr, pmdp, orig_pmd); + return false; + } + + if (ref_count != map_count + 1) { set_pmd_at(mm, addr, pmdp, orig_pmd); return false; } @@ -3119,12 +3130,11 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, { VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); - - return false; + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); } static void remap_page(struct folio *folio, unsigned long nr, int flags) diff --git a/mm/rmap.c b/mm/rmap.c index 3ef659310797..72907eb1b8fe 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1724,9 +1724,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, } if (!pvmw.pte) { - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, - folio)) - goto walk_done; + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) + goto walk_done; + /* + * unmap_huge_pmd_locked has either already marked + * the folio as swap-backed or decided to retain it + * due to GUP or speculative references. + */ + goto walk_abort; + } if (flags & TTU_SPLIT_HUGE_PMD) { /*
On Tue, Jan 14, 2025 at 12:09 PM Barry Song <21cnbao@gmail.com> wrote: > > On Tue, Jan 14, 2025 at 4:40 PM Baolin Wang <baolin.wang@linux.alibaba.com> wrote: > > > > > > > > On 2025/1/13 11:39, Barry Song wrote: > > > From: Barry Song <v-songbaohua@oppo.com> > > > > > > The try_to_unmap_one() function currently handles PMD-mapped THPs > > > inefficiently. It first splits the PMD into PTEs, copies the dirty > > > state from the PMD to the PTEs, iterates over the PTEs to locate > > > the dirty state, and then marks the THP as swap-backed. This process > > > involves unnecessary PMD splitting and redundant iteration. Instead, > > > this functionality can be efficiently managed in > > > __discard_anon_folio_pmd_locked(), avoiding the extra steps and > > > improving performance. > > > > > > The following microbenchmark redirties folios after invoking MADV_FREE, > > > then measures the time taken to perform memory reclamation (actually > > > set those folios swapbacked again) on the redirtied folios. > > > > > > #include <stdio.h> > > > #include <sys/mman.h> > > > #include <string.h> > > > #include <time.h> > > > > > > #define SIZE 128*1024*1024 // 128 MB > > > > > > int main(int argc, char *argv[]) > > > { > > > while(1) { > > > volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, > > > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > > > > > memset((void *)p, 1, SIZE); > > > madvise((void *)p, SIZE, MADV_FREE); > > > /* redirty after MADV_FREE */ > > > memset((void *)p, 1, SIZE); > > > > > > clock_t start_time = clock(); > > > madvise((void *)p, SIZE, MADV_PAGEOUT); > > > clock_t end_time = clock(); > > > > > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > > > printf("Time taken by reclamation: %f seconds\n", elapsed_time); > > > > > > munmap((void *)p, SIZE); > > > } > > > return 0; > > > } > > > > > > Testing results are as below, > > > w/o patch: > > > ~ # ./a.out > > > Time taken by reclamation: 0.007300 seconds > > > Time taken by reclamation: 0.007226 seconds > > > Time taken by reclamation: 0.007295 seconds > > > Time taken by reclamation: 0.007731 seconds > > > Time taken by reclamation: 0.007134 seconds > > > Time taken by reclamation: 0.007285 seconds > > > Time taken by reclamation: 0.007720 seconds > > > Time taken by reclamation: 0.007128 seconds > > > Time taken by reclamation: 0.007710 seconds > > > Time taken by reclamation: 0.007712 seconds > > > Time taken by reclamation: 0.007236 seconds > > > Time taken by reclamation: 0.007690 seconds > > > Time taken by reclamation: 0.007174 seconds > > > Time taken by reclamation: 0.007670 seconds > > > Time taken by reclamation: 0.007169 seconds > > > Time taken by reclamation: 0.007305 seconds > > > Time taken by reclamation: 0.007432 seconds > > > Time taken by reclamation: 0.007158 seconds > > > Time taken by reclamation: 0.007133 seconds > > > … > > > > > > w/ patch > > > > > > ~ # ./a.out > > > Time taken by reclamation: 0.002124 seconds > > > Time taken by reclamation: 0.002116 seconds > > > Time taken by reclamation: 0.002150 seconds > > > Time taken by reclamation: 0.002261 seconds > > > Time taken by reclamation: 0.002137 seconds > > > Time taken by reclamation: 0.002173 seconds > > > Time taken by reclamation: 0.002063 seconds > > > Time taken by reclamation: 0.002088 seconds > > > Time taken by reclamation: 0.002169 seconds > > > Time taken by reclamation: 0.002124 seconds > > > Time taken by reclamation: 0.002111 seconds > > > Time taken by reclamation: 0.002224 seconds > > > Time taken by reclamation: 0.002297 seconds > > > Time taken by reclamation: 0.002260 seconds > > > Time taken by reclamation: 0.002246 seconds > > > Time taken by reclamation: 0.002272 seconds > > > Time taken by reclamation: 0.002277 seconds > > > Time taken by reclamation: 0.002462 seconds > > > … > > > > > > This patch significantly speeds up try_to_unmap_one() by allowing it > > > to skip redirtied THPs without splitting the PMD. > > > > > > Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com> > > > Suggested-by: Lance Yang <ioworker0@gmail.com> > > > Signed-off-by: Barry Song <v-songbaohua@oppo.com> > > > --- > > > mm/huge_memory.c | 17 ++++++++++++++--- > > > mm/rmap.c | 11 ++++++++++- > > > 2 files changed, 24 insertions(+), 4 deletions(-) > > > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index 3d3ebdc002d5..aea49f7125f1 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > > > int ref_count, map_count; > > > pmd_t orig_pmd = *pmdp; > > > > > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > > > + if (pmd_dirty(orig_pmd)) > > > + folio_set_dirty(folio); > > > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > > > + folio_set_swapbacked(folio); > > > return false; > > > + } > > > > > > orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > > > > > > @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > > > * > > > * The only folio refs must be one from isolation plus the rmap(s). > > > */ > > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > > > - ref_count != map_count + 1) { > > > + if (pmd_dirty(orig_pmd)) > > > + folio_set_dirty(folio); > > > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > > > + folio_set_swapbacked(folio); > > > + set_pmd_at(mm, addr, pmdp, orig_pmd); > > > + return false; > > > + } > > > + > > > + if (ref_count != map_count + 1) { > > > set_pmd_at(mm, addr, pmdp, orig_pmd); > > > return false; > > > } > > > diff --git a/mm/rmap.c b/mm/rmap.c > > > index 3ef659310797..02c4e4b2cd7b 100644 > > > --- a/mm/rmap.c > > > +++ b/mm/rmap.c > > > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > > > pte_t pteval; > > > struct page *subpage; > > > - bool anon_exclusive, ret = true; > > > + bool anon_exclusive, lazyfree, ret = true; > > > struct mmu_notifier_range range; > > > enum ttu_flags flags = (enum ttu_flags)(long)arg; > > > int nr_pages = 1; > > > @@ -1724,9 +1724,18 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > > } > > > > > > if (!pvmw.pte) { > > > + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); > > > > You've checked lazyfree here, so can we remove the duplicate check in > > unmap_huge_pmd_locked()? Then the code should be: > > > > if (lazyfree && unmap_huge_pmd_locked(...)) > > goto walk_done; > > > right. it seems unmap_huge_pmd_locked() only handles lazyfree pmd-mapped > thp. so i guess the code could be: Yep, it would be better to remove the duplicate check in unmap_huge_pmd_locked(), and we can extend unmap_huge_pmd_locked() in the future if needed. Thanks, Lance > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index aea49f7125f1..c4c3a7896de4 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3131,11 +3131,10 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); > VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); > + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); > + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); > > - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > - > - return false; > + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > } > > static void remap_page(struct folio *folio, unsigned long nr, int flags) > diff --git a/mm/rmap.c b/mm/rmap.c > index 02c4e4b2cd7b..72907eb1b8fe 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > pte_t pteval; > struct page *subpage; > - bool anon_exclusive, lazyfree, ret = true; > + bool anon_exclusive, ret = true; > struct mmu_notifier_range range; > enum ttu_flags flags = (enum ttu_flags)(long)arg; > int nr_pages = 1; > @@ -1724,18 +1724,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte) { > - lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); > - > - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > - folio)) > - goto walk_done; > - /* > - * unmap_huge_pmd_locked has either already marked > - * the folio as swap-backed or decided to retain it > - * due to GUP or speculative references. > - */ > - if (lazyfree) > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { > + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) > + goto walk_done; > + /* > + * unmap_huge_pmd_locked has either already marked > + * the folio as swap-backed or decided to retain it > + * due to GUP or speculative references. > + */ > goto walk_abort; > + } > > if (flags & TTU_SPLIT_HUGE_PMD) { > /* > > > > > > if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > > > folio)) > > > goto walk_done; > > > + /* > > > + * unmap_huge_pmd_locked has either already marked > > > + * the folio as swap-backed or decided to retain it > > > + * due to GUP or speculative references. > > > + */ > > > + if (lazyfree) > > > + goto walk_abort; > > > > > > if (flags & TTU_SPLIT_HUGE_PMD) { > > > /*
On 2025/1/14 14:00, Barry Song wrote: >>>> if (!pvmw.pte) { >>>> + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); >>> >>> You've checked lazyfree here, so can we remove the duplicate check in >>> unmap_huge_pmd_locked()? Then the code should be: >>> >>> if (lazyfree && unmap_huge_pmd_locked(...)) >>> goto walk_done; >> >> >> right. it seems unmap_huge_pmd_locked() only handles lazyfree pmd-mapped >> thp. so i guess the code could be: >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index aea49f7125f1..c4c3a7896de4 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3131,11 +3131,10 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, >> VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); >> VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); >> + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); >> + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); >> >> - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) >> - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); >> - >> - return false; >> + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); >> } >> >> static void remap_page(struct folio *folio, unsigned long nr, int flags) >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 02c4e4b2cd7b..72907eb1b8fe 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); >> pte_t pteval; >> struct page *subpage; >> - bool anon_exclusive, lazyfree, ret = true; >> + bool anon_exclusive, ret = true; >> struct mmu_notifier_range range; >> enum ttu_flags flags = (enum ttu_flags)(long)arg; >> int nr_pages = 1; >> @@ -1724,18 +1724,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> } >> >> if (!pvmw.pte) { >> - lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); >> - >> - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, >> - folio)) >> - goto walk_done; >> - /* >> - * unmap_huge_pmd_locked has either already marked >> - * the folio as swap-backed or decided to retain it >> - * due to GUP or speculative references. >> - */ >> - if (lazyfree) >> + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { >> + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) >> + goto walk_done; >> + /* >> + * unmap_huge_pmd_locked has either already marked >> + * the folio as swap-backed or decided to retain it >> + * due to GUP or speculative references. >> + */ >> goto walk_abort; >> + } >> >> if (flags & TTU_SPLIT_HUGE_PMD) { >> /* >> >>> >>>> if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, >>>> folio)) >>>> goto walk_done; >>>> + /* >>>> + * unmap_huge_pmd_locked has either already marked >>>> + * the folio as swap-backed or decided to retain it >>>> + * due to GUP or speculative references. >>>> + */ >>>> + if (lazyfree) >>>> + goto walk_abort; >>>> >>>> if (flags & TTU_SPLIT_HUGE_PMD) { >>>> /* > > > > The final diff is as follows. > Baolin, do you have any additional comments before I send out v3? No other comments. Look good to me.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 3d3ebdc002d5..aea49f7125f1 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, int ref_count, map_count; pmd_t orig_pmd = *pmdp; - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); return false; + } orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, * * The only folio refs must be one from isolation plus the rmap(s). */ - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || - ref_count != map_count + 1) { + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); + set_pmd_at(mm, addr, pmdp, orig_pmd); + return false; + } + + if (ref_count != map_count + 1) { set_pmd_at(mm, addr, pmdp, orig_pmd); return false; } diff --git a/mm/rmap.c b/mm/rmap.c index 3ef659310797..02c4e4b2cd7b 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); pte_t pteval; struct page *subpage; - bool anon_exclusive, ret = true; + bool anon_exclusive, lazyfree, ret = true; struct mmu_notifier_range range; enum ttu_flags flags = (enum ttu_flags)(long)arg; int nr_pages = 1; @@ -1724,9 +1724,18 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, } if (!pvmw.pte) { + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) goto walk_done; + /* + * unmap_huge_pmd_locked has either already marked + * the folio as swap-backed or decided to retain it + * due to GUP or speculative references. + */ + if (lazyfree) + goto walk_abort; if (flags & TTU_SPLIT_HUGE_PMD) { /*