lkml.org 
[lkml]   [2024]   [Apr]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 10/10] mm: page_alloc: consolidate free page accounting
    On Mon, Apr 08, 2024 at 09:38:20AM +0200, Vlastimil Babka wrote:
    > On 4/7/24 12:19 PM, Baolin Wang wrote:
    > > On 2024/3/21 02:02, Johannes Weiner wrote:
    > >>
    > >> + account_freepages(page, zone, 1 << order, migratetype);
    > >> +
    > >> while (order < MAX_PAGE_ORDER) {
    > >> - if (compaction_capture(capc, page, order, migratetype)) {
    > >> - __mod_zone_freepage_state(zone, -(1 << order),
    > >> - migratetype);
    > >> + int buddy_mt = migratetype;
    > >> +
    > >> + if (compaction_capture(capc, page, order, migratetype))
    > >> return;
    > >> - }
    > >
    > > IIUC, if the released page is captured by compaction, then the
    > > statistics for free pages should be correspondingly decreased,
    > > otherwise, there will be a slight regression for my thpcompact benchmark.
    > >
    > > thpcompact Percentage Faults Huge
    > > k6.9-rc2-base base + patch10 + 2 fixes
    > > Percentage huge-1 78.18 ( 0.00%) 71.92 ( -8.01%)
    > > Percentage huge-3 86.70 ( 0.00%) 86.07 ( -0.73%)
    > > Percentage huge-5 90.26 ( 0.00%) 78.02 ( -13.57%)
    > > Percentage huge-7 92.34 ( 0.00%) 78.67 ( -14.81%)
    > > Percentage huge-12 91.18 ( 0.00%) 81.04 ( -11.12%)
    > > Percentage huge-18 89.00 ( 0.00%) 79.57 ( -10.60%)
    > > Percentage huge-24 90.52 ( 0.00%) 80.07 ( -11.54%)
    > > Percentage huge-30 94.44 ( 0.00%) 96.28 ( 1.95%)
    > > Percentage huge-32 93.09 ( 0.00%) 99.39 ( 6.77%)
    > >
    > > I add below fix based on your fix 2, then the thpcompact Percentage
    > > looks good. How do you think for the fix?
    >
    > Yeah another well spotted, thanks. "slight regression" is an understatement,
    > this affects not just a "statistics" but very important counter
    > NR_FREE_PAGES which IIUC would eventually become larger than reality, make
    > the watermark checks false positive and result in depleted reserves etc etc.
    > Actually wondering why we're not seeing -next failures already (or maybe I
    > just haven't noticed).

    Good catch indeed.

    Trying to understand why I didn't notice this during testing, and I
    think it's because I had order-10 pageblocks in my config. There is
    this in compaction_capture():

    if (order < pageblock_order && migratetype == MIGRATE_MOVABLE)
    return false;

    Most compaction is for order-9 THPs on movable blocks, so I didn't get
    much capturing in practice in order for that leak to be noticable.

    In earlier versions of the patches I had more aggressive capturing,
    but also did the accounting in add_page_to/del_page_from_freelist(),
    so capturing only steals what's already accounted to be off list.

    With the __add/__del and the consolidated account_freepages()
    optimization, compaction_capture() needs explicit accounting again.

    > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > > index 8330c5c2de6b..2facf844ef84 100644
    > > --- a/mm/page_alloc.c
    > > +++ b/mm/page_alloc.c
    > > @@ -805,8 +805,10 @@ static inline void __free_one_page(struct page *page,
    > > while (order < MAX_PAGE_ORDER) {
    > > int buddy_mt = migratetype;
    > >
    > > - if (compaction_capture(capc, page, order, migratetype))
    > > + if (compaction_capture(capc, page, order, migratetype)) {
    > > + account_freepages(zone, -(1 << order), migratetype);
    > > return;
    > > + }
    > >
    > > buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
    > > if (!buddy)
    > >
    > > With my fix, the THP percentage looks better:
    > > k6.9-rc2-base base + patch10 + 2 fixes +
    > > my fix
    > > Percentage huge-1 78.18 ( 0.00%) 82.83 ( 5.94%)
    > > Percentage huge-3 86.70 ( 0.00%) 93.47 ( 7.81%)
    > > Percentage huge-5 90.26 ( 0.00%) 94.73 ( 4.95%)
    > > Percentage huge-7 92.34 ( 0.00%) 95.22 ( 3.12%)
    > > Percentage huge-12 91.18 ( 0.00%) 92.40 ( 1.34%)
    > > Percentage huge-18 89.00 ( 0.00%) 85.39 ( -4.06%)
    > > Percentage huge-24 90.52 ( 0.00%) 94.70 ( 4.61%)
    > > Percentage huge-30 94.44 ( 0.00%) 97.00 ( 2.71%)
    > > Percentage huge-32 93.09 ( 0.00%) 92.87 ( -0.24%)

    Acked-by: Johannes Weiner <hannes@cmpxchg.org>

    With fixed indentation:

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 70f82635f650..96815e3c22f2 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -805,8 +805,10 @@ static inline void __free_one_page(struct page *page,
    while (order < MAX_PAGE_ORDER) {
    int buddy_mt = migratetype;

    - if (compaction_capture(capc, page, order, migratetype))
    + if (compaction_capture(capc, page, order, migratetype)) {
    + account_freepages(zone, -(1 << order), migratetype);
    return;
    + }

    buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
    if (!buddy)
    \
     
     \ /
      Last update: 2024-05-27 16:28    [W:2.331 / U:0.324 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site