| Message ID | 20190610111252.239156-2-minchan@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Introduce MADV_COLD and MADV_PAGEOUT | expand |
On Mon 10-06-19 20:12:48, Minchan Kim wrote: > When a process expects no accesses to a certain memory range, it could > give a hint to kernel that the pages can be reclaimed when memory pressure > happens but data should be preserved for future use. This could reduce > workingset eviction so it ends up increasing performance. > > This patch introduces the new MADV_COLD hint to madvise(2) syscall. > MADV_COLD can be used by a process to mark a memory range as not expected > to be used in the near future. The hint can help kernel in deciding which > pages to evict early during memory pressure. > > It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves > > active file page -> inactive file LRU > active anon page -> inacdtive anon LRU > > Unlike MADV_FREE, it doesn't move active anonymous pages to inactive > file LRU's head because MADV_COLD is a little bit different symantic. > MADV_FREE means it's okay to discard when the memory pressure because > the content of the page is *garbage* so freeing such pages is almost zero > overhead since we don't need to swap out and access afterward causes just > minor fault. Thus, it would make sense to put those freeable pages in > inactive file LRU to compete other used-once pages. It makes sense for > implmentaion point of view, too because it's not swapbacked memory any > longer until it would be re-dirtied. Even, it could give a bonus to make > them be reclaimed on swapless system. However, MADV_COLD doesn't mean > garbage so reclaiming them requires swap-out/in in the end so it's bigger > cost. Since we have designed VM LRU aging based on cost-model, anonymous > cold pages would be better to position inactive anon's LRU list, not file > LRU. Furthermore, it would help to avoid unnecessary scanning if system > doesn't have a swap device. Let's start simpler way without adding > complexity at this moment. I would only add that it is a caveat that workloads with a lot of page cache are likely to ignore MADV_COLD on anonymous memory because we rarely age anonymous LRU lists. [...] > +static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr, > + unsigned long end, struct mm_walk *walk) > +{ This is duplicating a large part of madvise_free_pte_range with some subtle differences which are not explained anywhere (e.g. why does madvise_free_huge_pmd need try_lock on a page while not here? etc.). Why cannot we reuse a large part of that code and differ essentially on the reclaim target check and action? Have you considered to consolidate the code to share as much as possible? Maybe that is easier said than done because the devil is always in details... I would definitely feel much more comfortable to review the code without thinking about all those subtle details that have been already solved before. Especially all the THP ones. Other than that the patch looks sane to me. > + struct mmu_gather *tlb = walk->private; > + struct mm_struct *mm = tlb->mm; > + struct vm_area_struct *vma = walk->vma; > + pte_t *orig_pte, *pte, ptent; > + spinlock_t *ptl; > + struct page *page; > + unsigned long next; > + > + next = pmd_addr_end(addr, end); > + if (pmd_trans_huge(*pmd)) { > + pmd_t orig_pmd; > + > + tlb_change_page_size(tlb, HPAGE_PMD_SIZE); > + ptl = pmd_trans_huge_lock(pmd, vma); > + if (!ptl) > + return 0; > + > + orig_pmd = *pmd; > + if (is_huge_zero_pmd(orig_pmd)) > + goto huge_unlock; > + > + if (unlikely(!pmd_present(orig_pmd))) { > + VM_BUG_ON(thp_migration_supported() && > + !is_pmd_migration_entry(orig_pmd)); > + goto huge_unlock; > + } > + > + page = pmd_page(orig_pmd); > + if (next - addr != HPAGE_PMD_SIZE) { > + int err; > + > + if (page_mapcount(page) != 1) > + goto huge_unlock; > + > + get_page(page); > + spin_unlock(ptl); > + lock_page(page); > + err = split_huge_page(page); > + unlock_page(page); > + put_page(page); > + if (!err) > + goto regular_page; > + return 0; > + } > + > + if (pmd_young(orig_pmd)) { > + pmdp_invalidate(vma, addr, pmd); > + orig_pmd = pmd_mkold(orig_pmd); > + > + set_pmd_at(mm, addr, pmd, orig_pmd); > + tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > + } > + > + test_and_clear_page_young(page); > + deactivate_page(page); > +huge_unlock: > + spin_unlock(ptl); > + return 0; > + } > + > + if (pmd_trans_unstable(pmd)) > + return 0; > + > +regular_page: > + tlb_change_page_size(tlb, PAGE_SIZE); > + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > + flush_tlb_batched_pending(mm); > + arch_enter_lazy_mmu_mode(); > + for (; addr < end; pte++, addr += PAGE_SIZE) { > + ptent = *pte; > + > + if (pte_none(ptent)) > + continue; > + > + if (!pte_present(ptent)) > + continue; > + > + page = vm_normal_page(vma, addr, ptent); > + if (!page) > + continue; > + > + if (pte_young(ptent)) { > + ptent = ptep_get_and_clear_full(mm, addr, pte, > + tlb->fullmm); > + ptent = pte_mkold(ptent); > + set_pte_at(mm, addr, pte, ptent); > + tlb_remove_tlb_entry(tlb, pte, addr); > + } > + > + /* > + * We are deactivating a page for accelerating reclaiming. > + * VM couldn't reclaim the page unless we clear PG_young. > + * As a side effect, it makes confuse idle-page tracking > + * because they will miss recent referenced history. > + */ > + test_and_clear_page_young(page); > + deactivate_page(page); > + } > + > + arch_enter_lazy_mmu_mode(); > + pte_unmap_unlock(orig_pte, ptl); > + cond_resched(); > + > + return 0; > +}
On Wed, Jun 19, 2019 at 02:56:12PM +0200, Michal Hocko wrote: > On Mon 10-06-19 20:12:48, Minchan Kim wrote: > > When a process expects no accesses to a certain memory range, it could > > give a hint to kernel that the pages can be reclaimed when memory pressure > > happens but data should be preserved for future use. This could reduce > > workingset eviction so it ends up increasing performance. > > > > This patch introduces the new MADV_COLD hint to madvise(2) syscall. > > MADV_COLD can be used by a process to mark a memory range as not expected > > to be used in the near future. The hint can help kernel in deciding which > > pages to evict early during memory pressure. > > > > It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves > > > > active file page -> inactive file LRU > > active anon page -> inacdtive anon LRU > > > > Unlike MADV_FREE, it doesn't move active anonymous pages to inactive > > file LRU's head because MADV_COLD is a little bit different symantic. > > MADV_FREE means it's okay to discard when the memory pressure because > > the content of the page is *garbage* so freeing such pages is almost zero > > overhead since we don't need to swap out and access afterward causes just > > minor fault. Thus, it would make sense to put those freeable pages in > > inactive file LRU to compete other used-once pages. It makes sense for > > implmentaion point of view, too because it's not swapbacked memory any > > longer until it would be re-dirtied. Even, it could give a bonus to make > > them be reclaimed on swapless system. However, MADV_COLD doesn't mean > > garbage so reclaiming them requires swap-out/in in the end so it's bigger > > cost. Since we have designed VM LRU aging based on cost-model, anonymous > > cold pages would be better to position inactive anon's LRU list, not file > > LRU. Furthermore, it would help to avoid unnecessary scanning if system > > doesn't have a swap device. Let's start simpler way without adding > > complexity at this moment. > > I would only add that it is a caveat that workloads with a lot of page > cache are likely to ignore MADV_COLD on anonymous memory because we > rarely age anonymous LRU lists. Okay, I will add some more. > > [...] > > +static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr, > > + unsigned long end, struct mm_walk *walk) > > +{ > > This is duplicating a large part of madvise_free_pte_range with some > subtle differences which are not explained anywhere (e.g. why does > madvise_free_huge_pmd need try_lock on a page while not here? etc.). madvise_free_huge_pmd handle dirty bit but this is not. > > Why cannot we reuse a large part of that code and differ essentially on > the reclaim target check and action? Have you considered to consolidate > the code to share as much as possible? Maybe that is easier said than > done because the devil is always in details... Yub, it was not pretty when I tried. Please see last patch in this patchset.
On Thu 20-06-19 09:06:51, Minchan Kim wrote: > On Wed, Jun 19, 2019 at 02:56:12PM +0200, Michal Hocko wrote: [...] > > Why cannot we reuse a large part of that code and differ essentially on > > the reclaim target check and action? Have you considered to consolidate > > the code to share as much as possible? Maybe that is easier said than > > done because the devil is always in details... > > Yub, it was not pretty when I tried. Please see last patch in this > patchset. That is bad because this code is quite subtle - especially the THP part of it. I will be staring at the code some more. Maybe some simplification pops out.
On Thu, Jun 20, 2019 at 09:08:54AM +0200, Michal Hocko wrote: > On Thu 20-06-19 09:06:51, Minchan Kim wrote: > > On Wed, Jun 19, 2019 at 02:56:12PM +0200, Michal Hocko wrote: > [...] > > > Why cannot we reuse a large part of that code and differ essentially on > > > the reclaim target check and action? Have you considered to consolidate > > > the code to share as much as possible? Maybe that is easier said than > > > done because the devil is always in details... > > > > Yub, it was not pretty when I tried. Please see last patch in this > > patchset. > > That is bad because this code is quite subtle - especially the THP part > of it. I will be staring at the code some more. Maybe some > simplification pops out. Yeah, I couldn't come up with better idea. Actually, I wanted to be left. More suggestion to make simple/readable would be great.
diff --git a/include/linux/swap.h b/include/linux/swap.h index de2c67a33b7e..0ce997edb8bb 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -340,6 +340,7 @@ extern void lru_add_drain_cpu(int cpu); extern void lru_add_drain_all(void); extern void rotate_reclaimable_page(struct page *page); extern void deactivate_file_page(struct page *page); +extern void deactivate_page(struct page *page); extern void mark_page_lazyfree(struct page *page); extern void swap_setup(void); diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h index ef4623f03156..d7b4231eea63 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -47,6 +47,7 @@ #define MADV_SEQUENTIAL 2 /* expect sequential page references */ #define MADV_WILLNEED 3 /* will need these pages */ #define MADV_DONTNEED 4 /* don't need these pages */ +#define MADV_COLD 5 /* deactivatie these pages */ /* common parameters: try to keep these consistent across architectures */ #define MADV_FREE 8 /* free pages only if memory pressure */ diff --git a/mm/internal.h b/mm/internal.h index e32390802fd3..0d5f720c75ab 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -39,7 +39,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf); void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma, unsigned long floor, unsigned long ceiling); -static inline bool can_madv_dontneed_vma(struct vm_area_struct *vma) +static inline bool can_madv_lru_vma(struct vm_area_struct *vma) { return !(vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP)); } diff --git a/mm/madvise.c b/mm/madvise.c index 628022e674a7..67c0379f64a7 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -40,6 +40,7 @@ static int madvise_need_mmap_write(int behavior) case MADV_REMOVE: case MADV_WILLNEED: case MADV_DONTNEED: + case MADV_COLD: case MADV_FREE: return 0; default: @@ -307,6 +308,149 @@ static long madvise_willneed(struct vm_area_struct *vma, return 0; } +static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr, + unsigned long end, struct mm_walk *walk) +{ + struct mmu_gather *tlb = walk->private; + struct mm_struct *mm = tlb->mm; + struct vm_area_struct *vma = walk->vma; + pte_t *orig_pte, *pte, ptent; + spinlock_t *ptl; + struct page *page; + unsigned long next; + + next = pmd_addr_end(addr, end); + if (pmd_trans_huge(*pmd)) { + pmd_t orig_pmd; + + tlb_change_page_size(tlb, HPAGE_PMD_SIZE); + ptl = pmd_trans_huge_lock(pmd, vma); + if (!ptl) + return 0; + + orig_pmd = *pmd; + if (is_huge_zero_pmd(orig_pmd)) + goto huge_unlock; + + if (unlikely(!pmd_present(orig_pmd))) { + VM_BUG_ON(thp_migration_supported() && + !is_pmd_migration_entry(orig_pmd)); + goto huge_unlock; + } + + page = pmd_page(orig_pmd); + if (next - addr != HPAGE_PMD_SIZE) { + int err; + + if (page_mapcount(page) != 1) + goto huge_unlock; + + get_page(page); + spin_unlock(ptl); + lock_page(page); + err = split_huge_page(page); + unlock_page(page); + put_page(page); + if (!err) + goto regular_page; + return 0; + } + + if (pmd_young(orig_pmd)) { + pmdp_invalidate(vma, addr, pmd); + orig_pmd = pmd_mkold(orig_pmd); + + set_pmd_at(mm, addr, pmd, orig_pmd); + tlb_remove_pmd_tlb_entry(tlb, pmd, addr); + } + + test_and_clear_page_young(page); + deactivate_page(page); +huge_unlock: + spin_unlock(ptl); + return 0; + } + + if (pmd_trans_unstable(pmd)) + return 0; + +regular_page: + tlb_change_page_size(tlb, PAGE_SIZE); + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); + flush_tlb_batched_pending(mm); + arch_enter_lazy_mmu_mode(); + for (; addr < end; pte++, addr += PAGE_SIZE) { + ptent = *pte; + + if (pte_none(ptent)) + continue; + + if (!pte_present(ptent)) + continue; + + page = vm_normal_page(vma, addr, ptent); + if (!page) + continue; + + if (pte_young(ptent)) { + ptent = ptep_get_and_clear_full(mm, addr, pte, + tlb->fullmm); + ptent = pte_mkold(ptent); + set_pte_at(mm, addr, pte, ptent); + tlb_remove_tlb_entry(tlb, pte, addr); + } + + /* + * We are deactivating a page for accelerating reclaiming. + * VM couldn't reclaim the page unless we clear PG_young. + * As a side effect, it makes confuse idle-page tracking + * because they will miss recent referenced history. + */ + test_and_clear_page_young(page); + deactivate_page(page); + } + + arch_enter_lazy_mmu_mode(); + pte_unmap_unlock(orig_pte, ptl); + cond_resched(); + + return 0; +} + +static void madvise_cold_page_range(struct mmu_gather *tlb, + struct vm_area_struct *vma, + unsigned long addr, unsigned long end) +{ + struct mm_walk cold_walk = { + .pmd_entry = madvise_cold_pte_range, + .mm = vma->vm_mm, + .private = tlb, + }; + + tlb_start_vma(tlb, vma); + walk_page_range(addr, end, &cold_walk); + tlb_end_vma(tlb, vma); +} + +static long madvise_cold(struct vm_area_struct *vma, + struct vm_area_struct **prev, + unsigned long start_addr, unsigned long end_addr) +{ + struct mm_struct *mm = vma->vm_mm; + struct mmu_gather tlb; + + *prev = vma; + if (!can_madv_lru_vma(vma)) + return -EINVAL; + + lru_add_drain(); + tlb_gather_mmu(&tlb, mm, start_addr, end_addr); + madvise_cold_page_range(&tlb, vma, start_addr, end_addr); + tlb_finish_mmu(&tlb, start_addr, end_addr); + + return 0; +} + static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, struct mm_walk *walk) @@ -519,7 +663,7 @@ static long madvise_dontneed_free(struct vm_area_struct *vma, int behavior) { *prev = vma; - if (!can_madv_dontneed_vma(vma)) + if (!can_madv_lru_vma(vma)) return -EINVAL; if (!userfaultfd_remove(vma, start, end)) { @@ -541,7 +685,7 @@ static long madvise_dontneed_free(struct vm_area_struct *vma, */ return -ENOMEM; } - if (!can_madv_dontneed_vma(vma)) + if (!can_madv_lru_vma(vma)) return -EINVAL; if (end > vma->vm_end) { /* @@ -695,6 +839,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev, return madvise_remove(vma, prev, start, end); case MADV_WILLNEED: return madvise_willneed(vma, prev, start, end); + case MADV_COLD: + return madvise_cold(vma, prev, start, end); case MADV_FREE: case MADV_DONTNEED: return madvise_dontneed_free(vma, prev, start, end, behavior); @@ -716,6 +862,7 @@ madvise_behavior_valid(int behavior) case MADV_WILLNEED: case MADV_DONTNEED: case MADV_FREE: + case MADV_COLD: #ifdef CONFIG_KSM case MADV_MERGEABLE: case MADV_UNMERGEABLE: diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 5a58778c91d4..f73d5f5145f0 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -515,7 +515,7 @@ bool __oom_reap_task_mm(struct mm_struct *mm) set_bit(MMF_UNSTABLE, &mm->flags); for (vma = mm->mmap ; vma; vma = vma->vm_next) { - if (!can_madv_dontneed_vma(vma)) + if (!can_madv_lru_vma(vma)) continue; /* diff --git a/mm/swap.c b/mm/swap.c index 6d153ce4cb8c..7e44f5b50774 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -47,6 +47,7 @@ int page_cluster; static DEFINE_PER_CPU(struct pagevec, lru_add_pvec); static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs); static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs); +static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs); static DEFINE_PER_CPU(struct pagevec, lru_lazyfree_pvecs); #ifdef CONFIG_SMP static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs); @@ -538,6 +539,22 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec, update_page_reclaim_stat(lruvec, file, 0); } +static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec, + void *arg) +{ + if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) { + int file = page_is_file_cache(page); + int lru = page_lru_base_type(page); + + del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE); + ClearPageActive(page); + ClearPageReferenced(page); + add_page_to_lru_list(page, lruvec, lru); + + __count_vm_events(PGDEACTIVATE, hpage_nr_pages(page)); + update_page_reclaim_stat(lruvec, file, 0); + } +} static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, void *arg) @@ -590,6 +607,10 @@ void lru_add_drain_cpu(int cpu) if (pagevec_count(pvec)) pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL); + pvec = &per_cpu(lru_deactivate_pvecs, cpu); + if (pagevec_count(pvec)) + pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL); + pvec = &per_cpu(lru_lazyfree_pvecs, cpu); if (pagevec_count(pvec)) pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL); @@ -623,6 +644,26 @@ void deactivate_file_page(struct page *page) } } +/* + * deactivate_page - deactivate a page + * @page: page to deactivate + * + * deactivate_page() moves @page to the inactive list if @page was on the active + * list and was not an unevictable page. This is done to accelerate the reclaim + * of @page. + */ +void deactivate_page(struct page *page) +{ + if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) { + struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs); + + get_page(page); + if (!pagevec_add(pvec, page) || PageCompound(page)) + pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL); + put_cpu_var(lru_deactivate_pvecs); + } +} + /** * mark_page_lazyfree - make an anon page lazyfree * @page: page to deactivate @@ -687,6 +728,7 @@ void lru_add_drain_all(void) if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) || pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) || pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) || + pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) || pagevec_count(&per_cpu(lru_lazyfree_pvecs, cpu)) || need_activate_page_drain(cpu)) { INIT_WORK(work, lru_add_drain_per_cpu);
When a process expects no accesses to a certain memory range, it could give a hint to kernel that the pages can be reclaimed when memory pressure happens but data should be preserved for future use. This could reduce workingset eviction so it ends up increasing performance. This patch introduces the new MADV_COLD hint to madvise(2) syscall. MADV_COLD can be used by a process to mark a memory range as not expected to be used in the near future. The hint can help kernel in deciding which pages to evict early during memory pressure. It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves active file page -> inactive file LRU active anon page -> inacdtive anon LRU Unlike MADV_FREE, it doesn't move active anonymous pages to inactive file LRU's head because MADV_COLD is a little bit different symantic. MADV_FREE means it's okay to discard when the memory pressure because the content of the page is *garbage* so freeing such pages is almost zero overhead since we don't need to swap out and access afterward causes just minor fault. Thus, it would make sense to put those freeable pages in inactive file LRU to compete other used-once pages. It makes sense for implmentaion point of view, too because it's not swapbacked memory any longer until it would be re-dirtied. Even, it could give a bonus to make them be reclaimed on swapless system. However, MADV_COLD doesn't mean garbage so reclaiming them requires swap-out/in in the end so it's bigger cost. Since we have designed VM LRU aging based on cost-model, anonymous cold pages would be better to position inactive anon's LRU list, not file LRU. Furthermore, it would help to avoid unnecessary scanning if system doesn't have a swap device. Let's start simpler way without adding complexity at this moment. All of error rule is same with MADV_DONTNEED. * v1 * remove page_mapcount filter - hannes, mhocko * fix idle page handling - joelaf * RFCv2 * add more description - mhocko * RFCv1 * renaming from MADV_COOL to MADV_COLD - hannes * internal review * use clear_page_youn in deactivate_page - joelaf * Revise the description - surenb * Renaming from MADV_WARM to MADV_COOL - surenb Signed-off-by: Minchan Kim <minchan@kernel.org> --- include/linux/swap.h | 1 + include/uapi/asm-generic/mman-common.h | 1 + mm/internal.h | 2 +- mm/madvise.c | 151 ++++++++++++++++++++++++- mm/oom_kill.c | 2 +- mm/swap.c | 42 +++++++ 6 files changed, 195 insertions(+), 4 deletions(-)