Messages in this thread | | | Date | Wed, 10 Apr 2024 16:49:42 +0800 | Subject | Re: [PATCH 10/10] mm: page_alloc: consolidate free page accounting | From | Baolin Wang <> |
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On 2024/4/9 22:46, Zi Yan wrote: > On 9 Apr 2024, at 5:31, Baolin Wang wrote: > >> On 2024/4/8 22:23, Johannes Weiner wrote: >>> 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. >> >> This makes me wonder why not use 'cc->migratetype' for migratetype comparison, so that low-order (like mTHP) compaction can directly get the released pages, which could avoid some compaction scans without mixing the migratetype? >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 2facf844ef84..7a64020f8222 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -622,7 +622,7 @@ compaction_capture(struct capture_control *capc, struct page *page, >> * and vice-versa but no more than normal fallback logic which can >> * have trouble finding a high-order free page. >> */ >> - if (order < pageblock_order && migratetype == MIGRATE_MOVABLE) >> + if (order < pageblock_order && capc->cc->migratetype != migratetype) >> return false; >> >> capc->page = page; > > It is worth trying, since at the original patch time mTHP was not present and > not capturing any MIGRATE_MOVABLE makes sense. But with your change, the capture > will lose the opportunity of letting an unmovable request use a reclaimable > pageblock and vice-versa, like the comment says. Please change the comment > as well and we should monitor potential unmovable and reclaimable regression.
Yes, but I think this case is easy to solve. Anyway let me try to do some measurement for mTHP.
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