On Mon, Jun 03, 2019 at 04:39:11PM -0400, Johannes Weiner wrote:
> On Mon, Jun 03, 2019 at 02:36:55PM +0900, Minchan Kim wrote:
> > When a process expects no accesses to a certain memory range
> > for a long time, it could hint kernel that the pages can be
> > reclaimed instantly 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_PAGEOUT hint to madvise(2)
> > syscall. MADV_PAGEOUT can be used by a process to mark a memory
> > range as not expected to be used for a long time so that kernel
> > reclaims *any LRU* pages instantly. The hint can help kernel in deciding
> > which pages to evict proactively.
> >
> > All of error rule is same with MADV_DONTNEED.
> >
> > Note:
> > This hint works with only private pages(IOW, page_mapcount(page) < 2)
> > because shared page could have more chance to be accessed from other
> > processes sharing the page so that it could cause major fault soon,
> > which is inefficient.
> >
> > * RFC v2
> > * make reclaim_pages simple via factoring out isolate logic - hannes
> >
> > * RFCv1
> > * rename from MADV_COLD to MADV_PAGEOUT - hannes
> > * bail out if process is being killed - Hillf
> > * fix reclaim_pages bugs - Hillf
> >
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > ---
> > include/linux/swap.h | 1 +
> > include/uapi/asm-generic/mman-common.h | 1 +
> > mm/madvise.c | 126 +++++++++++++++++++++++++
> > mm/vmscan.c | 34 +++++++
> > 4 files changed, 162 insertions(+)
> >
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index 0ce997edb8bb..063c0c1e112b 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -365,6 +365,7 @@ extern int vm_swappiness;
> > extern int remove_mapping(struct address_space *mapping, struct page *page);
> > extern unsigned long vm_total_pages;
> >
> > +extern unsigned long reclaim_pages(struct list_head *page_list);
> > #ifdef CONFIG_NUMA
> > extern int node_reclaim_mode;
> > extern int sysctl_min_unmapped_ratio;
> > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> > index 1190f4e7f7b9..92e347a89ddc 100644
> > --- a/include/uapi/asm-generic/mman-common.h
> > +++ b/include/uapi/asm-generic/mman-common.h
> > @@ -44,6 +44,7 @@
> > #define MADV_WILLNEED 3 /* will need these pages */
> > #define MADV_DONTNEED 4 /* don't need these pages */
> > #define MADV_COLD 5 /* deactivatie these pages */
> > +#define MADV_PAGEOUT 6 /* reclaim 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/madvise.c b/mm/madvise.c
> > index ab158766858a..b010249cb8b6 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -41,6 +41,7 @@ static int madvise_need_mmap_write(int behavior)
> > case MADV_WILLNEED:
> > case MADV_DONTNEED:
> > case MADV_COLD:
> > + case MADV_PAGEOUT:
> > case MADV_FREE:
> > return 0;
> > default:
> > @@ -415,6 +416,128 @@ static long madvise_cold(struct vm_area_struct *vma,
> > return 0;
> > }
> >
> > +static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> > + unsigned long end, struct mm_walk *walk)
> > +{
> > + pte_t *orig_pte, *pte, ptent;
> > + spinlock_t *ptl;
> > + LIST_HEAD(page_list);
> > + struct page *page;
> > + int isolated = 0;
> > + struct vm_area_struct *vma = walk->vma;
> > + unsigned long next;
> > +
> > + if (fatal_signal_pending(current))
> > + return -EINTR;
> > +
> > + next = pmd_addr_end(addr, end);
> > + if (pmd_trans_huge(*pmd)) {
> > + ptl = pmd_trans_huge_lock(pmd, vma);
> > + if (!ptl)
> > + return 0;
> > +
> > + if (is_huge_zero_pmd(*pmd))
> > + goto huge_unlock;
> > +
> > + page = pmd_page(*pmd);
> > + if (page_mapcount(page) > 1)
> > + goto huge_unlock;
> > +
> > + if (next - addr != HPAGE_PMD_SIZE) {
> > + int err;
> > +
> > + 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 (isolate_lru_page(page))
> > + goto huge_unlock;
> > +
> > + list_add(&page->lru, &page_list);
> > +huge_unlock:
> > + spin_unlock(ptl);
> > + reclaim_pages(&page_list);
> > + return 0;
> > + }
> > +
> > + if (pmd_trans_unstable(pmd))
> > + return 0;
> > +regular_page:
> > + orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > + for (pte = orig_pte; addr < end; pte++, addr += PAGE_SIZE) {
> > + ptent = *pte;
> > + if (!pte_present(ptent))
> > + continue;
> > +
> > + page = vm_normal_page(vma, addr, ptent);
> > + if (!page)
> > + continue;
> > +
> > + if (page_mapcount(page) > 1)
> > + continue;
> > +
> > + if (isolate_lru_page(page))
> > + continue;
> > +
> > + isolated++;
> > + list_add(&page->lru, &page_list);
> > + if (isolated >= SWAP_CLUSTER_MAX) {
> > + pte_unmap_unlock(orig_pte, ptl);
> > + reclaim_pages(&page_list);
> > + isolated = 0;
> > + pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > + orig_pte = pte;
> > + }
> > + }
> > +
> > + pte_unmap_unlock(orig_pte, ptl);
> > + reclaim_pages(&page_list);
> > + cond_resched();
> > +
> > + return 0;
> > +}
> > +
> > +static void madvise_pageout_page_range(struct mmu_gather *tlb,
> > + struct vm_area_struct *vma,
> > + unsigned long addr, unsigned long end)
> > +{
> > + struct mm_walk warm_walk = {
> > + .pmd_entry = madvise_pageout_pte_range,
> > + .mm = vma->vm_mm,
> > + };
> > +
> > + tlb_start_vma(tlb, vma);
> > + walk_page_range(addr, end, &warm_walk);
> > + tlb_end_vma(tlb, vma);
> > +}
> > +
> > +
> > +static long madvise_pageout(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_pageout_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)
> >
> > @@ -805,6 +928,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
> > return madvise_willneed(vma, prev, start, end);
> > case MADV_COLD:
> > return madvise_cold(vma, prev, start, end);
> > + case MADV_PAGEOUT:
> > + return madvise_pageout(vma, prev, start, end);
> > case MADV_FREE:
> > case MADV_DONTNEED:
> > return madvise_dontneed_free(vma, prev, start, end, behavior);
> > @@ -827,6 +952,7 @@ madvise_behavior_valid(int behavior)
> > case MADV_DONTNEED:
> > case MADV_FREE:
> > case MADV_COLD:
> > + case MADV_PAGEOUT:
> > #ifdef CONFIG_KSM
> > case MADV_MERGEABLE:
> > case MADV_UNMERGEABLE:
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 56df55e8afcd..2c2cf442db58 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2136,6 +2136,40 @@ static void shrink_active_list(unsigned long nr_to_scan,
> > nr_deactivate, nr_rotated, sc->priority, file);
> > }
> >
> > +unsigned long reclaim_pages(struct list_head *page_list)
> > +{
> > + unsigned long nr_reclaimed = 0;
> > + LIST_HEAD(node_page_list);
> > + struct reclaim_stat dummy_stat;
> > + struct scan_control sc = {
> > + .gfp_mask = GFP_KERNEL,
> > + .priority = DEF_PRIORITY,
> > + .may_writepage = 1,
> > + .may_unmap = 1,
> > + .may_swap = 1,
> > + };
> > +
> > + while (!list_empty(page_list)) {
> > + struct page *page;
> > +
> > + page = lru_to_page(page_list);
> > + list_move(&page->lru, &node_page_list);
> > + nr_reclaimed += shrink_page_list(&node_page_list,
> > + page_pgdat(page),
> > + &sc, TTU_IGNORE_ACCESS,
> > + &dummy_stat, true);
> > + if (!list_empty(&node_page_list)) {
> > + struct page *page = lru_to_page(&node_page_list);
> > +
> > + list_del(&page->lru);
> > + putback_lru_page(page);
> > +
> > + }
> > + }
>
> Awesome, this is way more readable now. Thanks for the cleanup!
>
> Regarding the loop, for the vast majority of instances, pages on
> page_list will actually be from the same node. It would make sense to
> do batching here and collect pages until last_pgdat != pgdat. That
> should reduce the number of tlb flushes and memcg uncharge flushes in
> shrink_page_list().
Sure, Thanks!
