Re: [patch 5/5]thp: split huge page if head page is isolated
From: Shaohua Li
Date: Wed Nov 09 2011 - 02:01:24 EST
On Wed, 2011-11-09 at 14:28 +0800, Minchan Kim wrote:
> On Wed, Nov 09, 2011 at 01:27:55PM +0800, Shaohua Li wrote:
> > On Tue, 2011-11-08 at 16:59 +0800, Minchan Kim wrote:
> > > On Wed, Nov 02, 2011 at 11:17:55AM +0800, Shaohua Li wrote:
> > > > On Mon, 2011-10-31 at 17:03 +0800, Shaohua Li wrote:
> > > > > On Mon, 2011-10-31 at 16:23 +0800, Minchan Kim wrote:
> > > > > > On Mon, Oct 31, 2011 at 09:21:28AM +0800, Shaohua Li wrote:
> > > > > > > On Sat, 2011-10-29 at 08:06 +0800, Minchan Kim wrote:
> > > > > > > > On Tue, Oct 25, 2011 at 10:59:40AM +0800, Shaohua Li wrote:
> > > > > > > > > With current logic, if page reclaim finds a huge page, it will just reclaim
> > > > > > > > > the head page and leave tail pages reclaimed later. Let's take an example,
> > > > > > > > > lru list has page A and B, page A is huge page:
> > > > > > > > > 1. page A is isolated
> > > > > > > > > 2. page B is isolated
> > > > > > > > > 3. shrink_page_list() adds page A to swap page cache. so page A is split.
> > > > > > > > > page A+1, page A+2, ... are added to lru list.
> > > > > > > > > 4. shrink_page_list() adds page B to swap page cache.
> > > > > > > > > 5. page A and B is written out and reclaimed.
> > > > > > > > > 6. page A+1, A+2 ... is isolated and reclaimed later.
> > > > > > > > > So the reclaim order is A, B, ...(maybe other pages), A+1, A+2 ...
> > > > > > > > >
> > > > > > > > > We expected the whole huge page A is reclaimed in the meantime, so
> > > > > > > > > the order is A, A+1, ... A+HPAGE_PMD_NR-1, B, ....
> > > > > > > > >
> > > > > > > > > With this patch, we do huge page split just after the head page is isolated
> > > > > > > > > for inactive lru list, so the tail pages will be reclaimed immediately.
> > > > > > > > >
> > > > > > > > > In a test, a range of anonymous memory is written and will trigger swap.
> > > > > > > > > Without the patch:
> > > > > > > > > #cat /proc/vmstat|grep thp
> > > > > > > > > thp_fault_alloc 451
> > > > > > > > > thp_fault_fallback 0
> > > > > > > > > thp_collapse_alloc 0
> > > > > > > > > thp_collapse_alloc_failed 0
> > > > > > > > > thp_split 238
> > > > > > > > >
> > > > > > > > > With the patch:
> > > > > > > > > #cat /proc/vmstat|grep thp
> > > > > > > > > thp_fault_alloc 450
> > > > > > > > > thp_fault_fallback 1
> > > > > > > > > thp_collapse_alloc 0
> > > > > > > > > thp_collapse_alloc_failed 0
> > > > > > > > > thp_split 103
> > > > > > > > >
> > > > > > > > > So the thp_split number is reduced a lot, though there is one extra
> > > > > > > > > thp_fault_fallback.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> > > > > > > > > ---
> > > > > > > > > include/linux/memcontrol.h | 3 +-
> > > > > > > > > mm/memcontrol.c | 12 +++++++++--
> > > > > > > > > mm/vmscan.c | 49 ++++++++++++++++++++++++++++++++++-----------
> > > > > > > > > 3 files changed, 50 insertions(+), 14 deletions(-)
> > > > > > > > >
> > > > > > > > > Index: linux/mm/vmscan.c
> > > > > > > > > ===================================================================
> > > > > > > > > --- linux.orig/mm/vmscan.c 2011-10-25 08:36:08.000000000 +0800
> > > > > > > > > +++ linux/mm/vmscan.c 2011-10-25 09:51:44.000000000 +0800
> > > > > > > > > @@ -1076,7 +1076,8 @@ int __isolate_lru_page(struct page *page
> > > > > > > > > */
> > > > > > > > > static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> > > > > > > > > struct list_head *src, struct list_head *dst,
> > > > > > > > > - unsigned long *scanned, int order, int mode, int file)
> > > > > > > > > + unsigned long *scanned, int order, int mode, int file,
> > > > > > > > > + struct page **split_page)
> > > > > > > > > {
> > > > > > > > > unsigned long nr_taken = 0;
> > > > > > > > > unsigned long nr_lumpy_taken = 0;
> > > > > > > > > @@ -1100,7 +1101,12 @@ static unsigned long isolate_lru_pages(u
> > > > > > > > > case 0:
> > > > > > > > > list_move(&page->lru, dst);
> > > > > > > > > mem_cgroup_del_lru(page);
> > > > > > > > > - nr_taken += hpage_nr_pages(page);
> > > > > > > > > + if (PageTransHuge(page) && split_page) {
> > > > > > > > > + nr_taken++;
> > > > > > > > > + *split_page = page;
> > > > > > > > > + goto out;
> > > > > > > > > + } else
> > > > > > > > > + nr_taken += hpage_nr_pages(page);
> > > > > > > > > break;
> > > > > > > > >
> > > > > > > > > case -EBUSY:
> > > > > > > > > @@ -1158,11 +1164,16 @@ static unsigned long isolate_lru_pages(u
> > > > > > > > > if (__isolate_lru_page(cursor_page, mode, file) == 0) {
> > > > > > > > > list_move(&cursor_page->lru, dst);
> > > > > > > > > mem_cgroup_del_lru(cursor_page);
> > > > > > > > > - nr_taken += hpage_nr_pages(page);
> > > > > > > > > nr_lumpy_taken++;
> > > > > > > > > if (PageDirty(cursor_page))
> > > > > > > > > nr_lumpy_dirty++;
> > > > > > > > > scan++;
> > > > > > > > > + if (PageTransHuge(page) && split_page) {
> > > > > > > > > + nr_taken++;
> > > > > > > > > + *split_page = page;
> > > > > > > > > + goto out;
> > > > > > > > > + } else
> > > > > > > > > + nr_taken += hpage_nr_pages(page);
> > > > > > > > > } else {
> > > > > > > > > /*
> > > > > > > > > * Check if the page is freed already.
> > > > > > > > > @@ -1188,6 +1199,7 @@ static unsigned long isolate_lru_pages(u
> > > > > > > > > nr_lumpy_failed++;
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > +out:
> > > > > > > > > *scanned = scan;
> > > > > > > > >
> > > > > > > > > trace_mm_vmscan_lru_isolate(order,
> > > > > > > > > @@ -1202,7 +1214,8 @@ static unsigned long isolate_pages_globa
> > > > > > > > > struct list_head *dst,
> > > > > > > > > unsigned long *scanned, int order,
> > > > > > > > > int mode, struct zone *z,
> > > > > > > > > - int active, int file)
> > > > > > > > > + int active, int file,
> > > > > > > > > + struct page **split_page)
> > > > > > > > > {
> > > > > > > > > int lru = LRU_BASE;
> > > > > > > > > if (active)
> > > > > > > > > @@ -1210,7 +1223,7 @@ static unsigned long isolate_pages_globa
> > > > > > > > > if (file)
> > > > > > > > > lru += LRU_FILE;
> > > > > > > > > return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
> > > > > > > > > - mode, file);
> > > > > > > > > + mode, file, split_page);
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > /*
> > > > > > > > > @@ -1444,10 +1457,12 @@ shrink_inactive_list(unsigned long nr_to
> > > > > > > > > {
> > > > > > > > > LIST_HEAD(page_list);
> > > > > > > > > unsigned long nr_scanned;
> > > > > > > > > + unsigned long total_scanned = 0;
> > > > > > > > > unsigned long nr_reclaimed = 0;
> > > > > > > > > unsigned long nr_taken;
> > > > > > > > > unsigned long nr_anon;
> > > > > > > > > unsigned long nr_file;
> > > > > > > > > + struct page *split_page;
> > > > > > > > >
> > > > > > > > > while (unlikely(too_many_isolated(zone, file, sc))) {
> > > > > > > > > congestion_wait(BLK_RW_ASYNC, HZ/10);
> > > > > > > > > @@ -1458,16 +1473,19 @@ shrink_inactive_list(unsigned long nr_to
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > set_reclaim_mode(priority, sc, false);
> > > > > > > > > +again:
> > > > > > > > > lru_add_drain();
> > > > > > > > > + split_page = NULL;
> > > > > > > > > spin_lock_irq(&zone->lru_lock);
> > > > > > > > >
> > > > > > > > > if (scanning_global_lru(sc)) {
> > > > > > > > > - nr_taken = isolate_pages_global(nr_to_scan,
> > > > > > > > > + nr_taken = isolate_pages_global(nr_to_scan - total_scanned,
> > > > > > > > > &page_list, &nr_scanned, sc->order,
> > > > > > > > > sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
> > > > > > > > > ISOLATE_BOTH : ISOLATE_INACTIVE,
> > > > > > > > > - zone, 0, file);
> > > > > > > > > + zone, 0, file, &split_page);
> > > > > > > > > zone->pages_scanned += nr_scanned;
> > > > > > > > > + total_scanned += nr_scanned;
> > > > > > > > > if (current_is_kswapd())
> > > > > > > > > __count_zone_vm_events(PGSCAN_KSWAPD, zone,
> > > > > > > > > nr_scanned);
> > > > > > > > > @@ -1475,12 +1493,13 @@ shrink_inactive_list(unsigned long nr_to
> > > > > > > > > __count_zone_vm_events(PGSCAN_DIRECT, zone,
> > > > > > > > > nr_scanned);
> > > > > > > > > } else {
> > > > > > > > > - nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
> > > > > > > > > + nr_taken = mem_cgroup_isolate_pages(nr_to_scan - total_scanned,
> > > > > > > > > &page_list, &nr_scanned, sc->order,
> > > > > > > > > sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
> > > > > > > > > ISOLATE_BOTH : ISOLATE_INACTIVE,
> > > > > > > > > zone, sc->mem_cgroup,
> > > > > > > > > - 0, file);
> > > > > > > > > + 0, file, &split_page);
> > > > > > > > > + total_scanned += nr_scanned;
> > > > > > > > > /*
> > > > > > > > > * mem_cgroup_isolate_pages() keeps track of
> > > > > > > > > * scanned pages on its own.
> > > > > > > > > @@ -1491,11 +1510,19 @@ shrink_inactive_list(unsigned long nr_to
> > > > > > > > > spin_unlock_irq(&zone->lru_lock);
> > > > > > > > > return 0;
> > > > > > > > > }
> > > > > > > > > + if (split_page && total_scanned < nr_to_scan) {
> > > > > > > > > + spin_unlock_irq(&zone->lru_lock);
> > > > > > > > > + split_huge_page(split_page);
> > > > > > > > > + goto again;
> > > > > > > > > + }
> > > > > > > > >
> > > > > > > > > update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
> > > > > > > > >
> > > > > > > > > spin_unlock_irq(&zone->lru_lock);
> > > > > > > > >
> > > > > > > > > + if (split_page)
> > > > > > > > > + split_huge_page(split_page);
> > > > > > > > > +
> > > > > > > > > nr_reclaimed = shrink_page_list(&page_list, zone, sc);
> > > > > > > > >
> > > > > > > > > /* Check if we should syncronously wait for writeback */
> > > > > > > > > @@ -1589,13 +1616,13 @@ static void shrink_active_list(unsigned
> > > > > > > > > nr_taken = isolate_pages_global(nr_pages, &l_hold,
> > > > > > > > > &pgscanned, sc->order,
> > > > > > > > > ISOLATE_ACTIVE, zone,
> > > > > > > > > - 1, file);
> > > > > > > > > + 1, file, NULL);
> > > > > > > > > zone->pages_scanned += pgscanned;
> > > > > > > > > } else {
> > > > > > > > > nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
> > > > > > > > > &pgscanned, sc->order,
> > > > > > > > > ISOLATE_ACTIVE, zone,
> > > > > > > > > - sc->mem_cgroup, 1, file);
> > > > > > > > > + sc->mem_cgroup, 1, file, NULL);
> > > > > > > > > /*
> > > > > > > > > * mem_cgroup_isolate_pages() keeps track of
> > > > > > > > > * scanned pages on its own.
> > > > > > > > > Index: linux/mm/memcontrol.c
> > > > > > > > > ===================================================================
> > > > > > > > > --- linux.orig/mm/memcontrol.c 2011-10-25 08:36:08.000000000 +0800
> > > > > > > > > +++ linux/mm/memcontrol.c 2011-10-25 09:33:51.000000000 +0800
> > > > > > > > > @@ -1187,7 +1187,8 @@ unsigned long mem_cgroup_isolate_pages(u
> > > > > > > > > unsigned long *scanned, int order,
> > > > > > > > > int mode, struct zone *z,
> > > > > > > > > struct mem_cgroup *mem_cont,
> > > > > > > > > - int active, int file)
> > > > > > > > > + int active, int file,
> > > > > > > > > + struct page **split_page)
> > > > > > > > > {
> > > > > > > > > unsigned long nr_taken = 0;
> > > > > > > > > struct page *page;
> > > > > > > > > @@ -1224,7 +1225,13 @@ unsigned long mem_cgroup_isolate_pages(u
> > > > > > > > > case 0:
> > > > > > > > > list_move(&page->lru, dst);
> > > > > > > > > mem_cgroup_del_lru(page);
> > > > > > > > > - nr_taken += hpage_nr_pages(page);
> > > > > > > > > + if (PageTransHuge(page) && split_page) {
> > > > > > > > > + nr_taken++;
> > > > > > > > > + *split_page = page;
> > > > > > > > > + goto out;
> > > > > > > > > + } else
> > > > > > > > > + nr_taken += hpage_nr_pages(page);
> > > > > > > > > +
> > > > > > > > > break;
> > > > > > > > > case -EBUSY:
> > > > > > > > > /* we don't affect global LRU but rotate in our LRU */
> > > > > > > > > @@ -1235,6 +1242,7 @@ unsigned long mem_cgroup_isolate_pages(u
> > > > > > > > > }
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > +out:
> > > > > > > > > *scanned = scan;
> > > > > > > > >
> > > > > > > > > trace_mm_vmscan_memcg_isolate(0, nr_to_scan, scan, nr_taken,
> > > > > > > > > Index: linux/include/linux/memcontrol.h
> > > > > > > > > ===================================================================
> > > > > > > > > --- linux.orig/include/linux/memcontrol.h 2011-10-25 08:36:08.000000000 +0800
> > > > > > > > > +++ linux/include/linux/memcontrol.h 2011-10-25 09:33:51.000000000 +0800
> > > > > > > > > @@ -37,7 +37,8 @@ extern unsigned long mem_cgroup_isolate_
> > > > > > > > > unsigned long *scanned, int order,
> > > > > > > > > int mode, struct zone *z,
> > > > > > > > > struct mem_cgroup *mem_cont,
> > > > > > > > > - int active, int file);
> > > > > > > > > + int active, int file,
> > > > > > > > > + struct page **split_page);
> > > > > > > > >
> > > > > > > > > #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > > > > > > > /*
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > > I saw the code. my concern is your patch could make unnecessary split of THP.
> > > > > > > >
> > > > > > > > When we isolates page, we can't know whether it's working set or not.
> > > > > > > > So split should happen after we judge it's working set page.
> > > > > > > yes, but since memory is big currently, it's unlikely the isolated page
> > > > > > > get accessed in the window. And I only did the split in
> > > > > >
> > > > > > We don't check page_reference when isolate happens.
> > > > > > Window which between isolation time and reclaim?
> > > > > > No. Window is from inactive's head to tail and it's the basic concept of
> > > > > > our LRU.
> > > > > >
> > > > > > > shrink_inactive_list, not in active list.
> > > > > >
> > > > > > But inactive list's size could be still big and
> > > > > > page reference heuristic is very important for reclaim algorithm.
> > > > > I mean pages aren't referenced. but ok, I can't take such assumption.
> > > > >
> > > > > > > And THP has mechanism to collapse small pages to huge page later.
> > > > > >
> > > > > > You mean "merge" instead of "collapse"?
> > > > > >
> > > > > > >
> > > > > > > > If you really want to merge this patch, I suggest that
> > > > > > > > we can handle it in shrink_page_list step, not isolation step.
> > > > > > > >
> > > > > > > > My totally untested code which is just to show the concept is as follows,
> > > > > > > I did consider this option before. It has its problem too. The isolation
> > > > > > > can isolate several huge page one time. And then later shrink_page_list
> > > > > > > can swap several huge page one time, which is unfortunate. I'm pretty
> > > > > > > sure this method can't reduce the thp_split count in my test. It could
> > > > > >
> > > > > > I understand your point but approach isn't good to me.
> > > > > > Maybe we can check whether we are going on or not before other THP page split happens
> > > > > > in shrink_page_list. If we split THP page successfully, maybe we can skip another THP split.
> > > > > > Another idea is we can avoid split of THP unless high order reclaim happens or low order
> > > > > > high priority pressure happens.
> > > > > I agreed the split better be done at shrink_page_list, but we must avoid
> > > > > isolate too many pages. I'll check if I can have a better solution for
> > > > > next post.
> > > > Let me try again.
> > > >
> > > > Subject: thp: improve huge page reclaim -v2
> > > >
> > > > With transparent huge page enabled, huge page will be split if it will
> > > > be reclaimed. With current logic, if page reclaim finds a huge page,
> > > > it will just reclaim the head page and leave tail pages reclaimed later.
> > > > Let's take an example, lru list has page A and B, page A is huge page:
> > > > 1. page A is isolated
> > > > 2. page B is isolated
> > > > 3. shrink_page_list() adds page A to swap page cache. so page A is split.
> > > > page A+1, page A+2, ... are added to lru list.
> > > > 4. shrink_page_list() adds page B to swap page cache.
> > > > 5. page A and B is written out and reclaimed.
> > > > 6. page A+1, A+2 ... is isolated and reclaimed later.
> > > > So the reclaim order is A, B, ...(maybe other pages), A+1, A+2 ...
> > > > The worst case could be we isolate/split 32 huge pages to try to reclaim
> > > > a huge page, but we only the 32 head pages are reclaimed.
> > > >
> > > > We expected the whole huge page A is reclaimed in the meantime, so
> > > > the order is A, A+1, ... A+HPAGE_PMD_NR-1, B, .... This could reduce a lot
> > > > of unnecessary huge page split and improve the reclaim.
> > > >
> > > > With this patch, if a huge page is found in isolation, don't continue
> > > > isolation. Since if the huge page is reclaimed, we can reclaim more pages
> > > > than SWAP_CLUSTER_MAX. In shrink_page_list(), the huge page is split and
> > > > all tail pages will be added to the isolation list, so the tail pages can
> > > > be reclaimed immediately.
> > > >
> > > > The drawback is we might isolate less pages if a huge page is found. But
> > > > I thought the benefit is far more than the drawback.
> > > >
> > > > All code path are with PageTransHuge(), so should have no impact to normal
> > > > cases.
> > > >
> > > > In a test, a range of anonymous memory is written and will trigger swap.
> > > > Without the patch:
> > > > #cat /proc/vmstat|grep thp
> > > > thp_fault_alloc 451
> > > > thp_fault_fallback 0
> > > > thp_collapse_alloc 0
> > > > thp_collapse_alloc_failed 0
> > > > thp_split 238
> > > >
> > > > With the patch:
> > > > #cat /proc/vmstat|grep thp
> > > > thp_fault_alloc 451
> > > > thp_fault_fallback 0
> > > > thp_collapse_alloc 0
> > > > thp_collapse_alloc_failed 0
> > > > thp_split 76
> > > >
> > > > So the thp_split number is reduced a lot.
> > > >
> > > > v1->v2: Do the huge page split in shrink_page_list(). Some code are adopted from
> > > > Minchan's.
> > > >
> > > > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> > > >
> > > > ---
> > > > include/linux/huge_mm.h | 7 ++++++-
> > > > include/linux/memcontrol.h | 3 ++-
> > > > include/linux/swap.h | 3 ++-
> > > > mm/huge_memory.c | 14 ++++++++------
> > > > mm/memcontrol.c | 6 +++++-
> > > > mm/swap.c | 10 +++++++++-
> > > > mm/swap_state.c | 6 ------
> > > > mm/vmscan.c | 27 ++++++++++++++++++++-------
> > > > 8 files changed, 52 insertions(+), 24 deletions(-)
> > > >
> > > > Index: linux/include/linux/huge_mm.h
> > > > ===================================================================
> > > > --- linux.orig/include/linux/huge_mm.h 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/include/linux/huge_mm.h 2011-11-02 10:06:33.000000000 +0800
> > > > @@ -81,7 +81,12 @@ extern int copy_pte_range(struct mm_stru
> > > > extern int handle_pte_fault(struct mm_struct *mm,
> > > > struct vm_area_struct *vma, unsigned long address,
> > > > pte_t *pte, pmd_t *pmd, unsigned int flags);
> > > > -extern int split_huge_page(struct page *page);
> > > > +extern int split_huge_page_list(struct page *page, struct list_head *dst);
> > > > +static inline int split_huge_page(struct page *page)
> > > > +{
> > > > + return split_huge_page_list(page, NULL);
> > > > +}
> > > > +
> > > > extern void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd);
> > > > #define split_huge_page_pmd(__mm, __pmd) \
> > > > do { \
> > > > Index: linux/include/linux/swap.h
> > > > ===================================================================
> > > > --- linux.orig/include/linux/swap.h 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/include/linux/swap.h 2011-11-02 10:06:33.000000000 +0800
> > > > @@ -218,7 +218,8 @@ extern unsigned int nr_free_pagecache_pa
> > > > extern void __lru_cache_add(struct page *, enum lru_list lru);
> > > > extern void lru_cache_add_lru(struct page *, enum lru_list lru);
> > > > extern void lru_add_page_tail(struct zone* zone,
> > > > - struct page *page, struct page *page_tail);
> > > > + struct page *page, struct page *page_tail,
> > > > + struct list_head *dst);
> > > > extern void activate_page(struct page *);
> > > > extern void mark_page_accessed(struct page *);
> > > > extern void lru_add_drain(void);
> > > > Index: linux/mm/huge_memory.c
> > > > ===================================================================
> > > > --- linux.orig/mm/huge_memory.c 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/mm/huge_memory.c 2011-11-02 10:58:21.000000000 +0800
> > > > @@ -1159,7 +1159,8 @@ static int __split_huge_page_splitting(s
> > > > return ret;
> > > > }
> > > >
> > > > -static void __split_huge_page_refcount(struct page *page)
> > > > +static void __split_huge_page_refcount(struct page *page,
> > > > + struct list_head *list)
> > > > {
> > > > int i;
> > > > struct zone *zone = page_zone(page);
> > > > @@ -1229,7 +1230,7 @@ static void __split_huge_page_refcount(s
> > > >
> > > > mem_cgroup_split_huge_fixup(page, page_tail);
> > > >
> > > > - lru_add_page_tail(zone, page, page_tail);
> > > > + lru_add_page_tail(zone, page, page_tail, list);
> > > > }
> > > >
> > > > __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
> > > > @@ -1343,7 +1344,8 @@ static int __split_huge_page_map(struct
> > > >
> > > > /* must be called with anon_vma->root->mutex hold */
> > > > static void __split_huge_page(struct page *page,
> > > > - struct anon_vma *anon_vma)
> > > > + struct anon_vma *anon_vma,
> > > > + struct list_head *list)
> > > > {
> > > > int mapcount, mapcount2;
> > > > struct anon_vma_chain *avc;
> > > > @@ -1375,7 +1377,7 @@ static void __split_huge_page(struct pag
> > > > mapcount, page_mapcount(page));
> > > > BUG_ON(mapcount != page_mapcount(page));
> > > >
> > > > - __split_huge_page_refcount(page);
> > > > + __split_huge_page_refcount(page, list);
> > > >
> > > > mapcount2 = 0;
> > > > list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
> > > > @@ -1392,7 +1394,7 @@ static void __split_huge_page(struct pag
> > > > BUG_ON(mapcount != mapcount2);
> > > > }
> > > >
> > > > -int split_huge_page(struct page *page)
> > > > +int split_huge_page_list(struct page *page, struct list_head *list)
> > > > {
> > > > struct anon_vma *anon_vma;
> > > > int ret = 1;
> > > > @@ -1406,7 +1408,7 @@ int split_huge_page(struct page *page)
> > > > goto out_unlock;
> > > >
> > > > BUG_ON(!PageSwapBacked(page));
> > > > - __split_huge_page(page, anon_vma);
> > > > + __split_huge_page(page, anon_vma, list);
> > > > count_vm_event(THP_SPLIT);
> > > >
> > > > BUG_ON(PageCompound(page));
> > > > Index: linux/mm/swap.c
> > > > ===================================================================
> > > > --- linux.orig/mm/swap.c 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/mm/swap.c 2011-11-02 10:06:33.000000000 +0800
> > > > @@ -634,7 +634,8 @@ EXPORT_SYMBOL(__pagevec_release);
> > > >
> > > > /* used by __split_huge_page_refcount() */
> > > > void lru_add_page_tail(struct zone* zone,
> > > > - struct page *page, struct page *page_tail)
> > > > + struct page *page, struct page *page_tail,
> > > > + struct list_head *dst)
> > > > {
> > > > int active;
> > > > enum lru_list lru;
> > > > @@ -646,6 +647,13 @@ void lru_add_page_tail(struct zone* zone
> > > > VM_BUG_ON(PageLRU(page_tail));
> > > > VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
> > > >
> > > > + /* The huge page is isolated */
> > > > + if (dst) {
> > > > + get_page(page_tail);
> > > > + list_add_tail(&page_tail->lru, dst);
> > > > + return;
> > > > + }
> > > > +
> > > > SetPageLRU(page_tail);
> > > >
> > > > if (page_evictable(page_tail, NULL)) {
> > > > Index: linux/mm/swap_state.c
> > > > ===================================================================
> > > > --- linux.orig/mm/swap_state.c 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/mm/swap_state.c 2011-11-02 10:06:33.000000000 +0800
> > > > @@ -154,12 +154,6 @@ int add_to_swap(struct page *page)
> > > > if (!entry.val)
> > > > return 0;
> > > >
> > > > - if (unlikely(PageTransHuge(page)))
> > > > - if (unlikely(split_huge_page(page))) {
> > > > - swapcache_free(entry, NULL);
> > > > - return 0;
> > > > - }
> > > > -
> > > > /*
> > > > * Radix-tree node allocations from PF_MEMALLOC contexts could
> > > > * completely exhaust the page allocator. __GFP_NOMEMALLOC
> > > > Index: linux/mm/vmscan.c
> > > > ===================================================================
> > > > --- linux.orig/mm/vmscan.c 2011-11-02 09:48:16.000000000 +0800
> > > > +++ linux/mm/vmscan.c 2011-11-02 10:58:21.000000000 +0800
> > > > @@ -838,6 +838,10 @@ static unsigned long shrink_page_list(st
> > > > if (PageAnon(page) && !PageSwapCache(page)) {
> > > > if (!(sc->gfp_mask & __GFP_IO))
> > > > goto keep_locked;
> > > > + if (unlikely(PageTransHuge(page)))
> > > > + if (unlikely(split_huge_page_list(page,
> > > > + page_list)))
> > > > + goto activate_locked;
> > > > if (!add_to_swap(page))
> > > > goto activate_locked;
> > > > may_enter_fs = 1;
> > > > @@ -1076,7 +1080,8 @@ int __isolate_lru_page(struct page *page
> > > > */
> > > > static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> > > > struct list_head *src, struct list_head *dst,
> > > > - unsigned long *scanned, int order, int mode, int file)
> > > > + unsigned long *scanned, int order, int mode, int file,
> > > > + bool break_on_thp)
> > > > {
> > >
> > > Sorry for late response.
> > > These day, I am very busy for new job.
> > Thanks for your time.
>
> NP.
>
> >
> > > Still, I don't like surgery of isolation part.
> > > What if we isolate a THP page but it is working set page?
> > > Let's assume as follows
> > >
> > > 1. Ioslate 32 page
> > > 2. Unfortunately, 1st page is THP so isolate_lru_page isolates just a
> > > page(of course, it's 512 pages)
> > > 3. shrink_page_list see that it's working set page but page_list
> > > have just a page so it have to isolate pages once more with higher priority.
> > that's possible. we might scan more pages, but should not introduce more
> > THP split, since isolate stop at huge page. on the other hand, if
> > isolation doesn't break in huge page, we can't split it and reclaim it
> > as a whole immediately. I didn't get a way to make both sides good. I
> > still thought the benefit is bigger than the drawback.
>
> I really would like to fix the problem, too.
>
> >
> > > How about this?
> > >
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 9fdfce7..8121415 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -960,7 +960,15 @@ free_it:
> > > * appear not as the counts should be low
> > > */
> > > list_add(&page->lru, &free_pages);
> > > - continue;
> > > +
> > > + /*
> > > + * If we have reclaimed enough pages, let's cut it off.
> > > + * It could prevent unnecessary THP split.
> > > + */
> > > + if (nr_reclaimed >= sc->nr_to_reclaim)
> > > + break;
> > > + else
> > > + continue;
> > >
> > > cull_mlocked:
> > > if (PageSwapCache(page))
> > this doesn't work. the huge page is dirty, so can't be reclaimed
> > immediately.
>
>
> Coudn't we make both sides good?
>
> Here is my quick patch.
> How about this?
> It doesn't split THPs in page_list but still reclaims non-THPs so
> I think it doesn't changed old behavior a lot.
I like this idea, will do some test soon.
Thanks,
Shaohua
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