Messages in this thread Patch in this message | | | Date | Tue, 9 Apr 2024 17:31:08 +0800 | Subject | Re: [PATCH 10/10] mm: page_alloc: consolidate free page accounting | From | Baolin Wang <> |
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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;
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