The patch titled Subject: mm: compaction: avoid fast_isolate_freepages blindly choose improper pageblock has been added to the -mm mm-unstable branch. Its filename is mm-compaction-avoid-fast_isolate_freepages-blindly-choose-improper-pageblock.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-avoid-fast_isolate_freepages-blindly-choose-improper-pageblock.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Barry Song <21cnbao@xxxxxxxxx> Subject: mm: compaction: avoid fast_isolate_freepages blindly choose improper pageblock Date: Thu, 7 Dec 2023 00:00:54 +1300 Testing shows fast_isolate_freepages can blindly choose an unsuitable pageblock from time to time particularly while the min mark is used from XXX path: if (!page) { cc->fast_search_fail++; if (scan_start) { /* * Use the highest PFN found above min. If one was * not found, be pessimistic for direct compaction * and use the min mark. */ if (highest >= min_pfn) { page = pfn_to_page(highest); cc->free_pfn = highest; } else { if (cc->direct_compaction && pfn_valid(min_pfn)) { /* XXX */ page = pageblock_pfn_to_page(min_pfn, min(pageblock_end_pfn(min_pfn), zone_end_pfn(cc->zone)), cc->zone); cc->free_pfn = min_pfn; } } } } The reason is that no code is doing any check on the min_pfn min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1)); In contrast, slow path of isolate_freepages() is always skipping unsuitable pageblocks in a decent way. This issue doesn't happen quite often. When running 25 machines with 16GiB memory for one night, most of them can hit this unexpected code path. However the frequency isn't like many times per second. It might be one time in a couple of hours. Thus, it is very hard to measure the visible performance impact in my machines though the affection of choosing the unsuitable migration_target should be negative in theory. I feel it's still worth fixing this to at least make the code theoretically self-explanatory as it is quite odd an unsuitable migration_target can be still migration_target. Link: https://lkml.kernel.org/r/20231206110054.61617-1-v-songbaohua@xxxxxxxx Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx> Reported-by: Zhanyuan Hu <huzhanyuan@xxxxxxxx> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/compaction.c~mm-compaction-avoid-fast_isolate_freepages-blindly-choose-improper-pageblock +++ a/mm/compaction.c @@ -1611,6 +1611,9 @@ static void fast_isolate_freepages(struc min(pageblock_end_pfn(min_pfn), zone_end_pfn(cc->zone)), cc->zone); + if (page && !suitable_migration_target(cc, page)) + page = NULL; + cc->free_pfn = min_pfn; } } _ Patches currently in -mm which might be from 21cnbao@xxxxxxxxx are mm-page_owner-record-and-dump-free_pid-and-free_tgid.patch mm-compaction-avoid-fast_isolate_freepages-blindly-choose-improper-pageblock.patch