On 29 Oct 2020, at 17:14, Yang Shi wrote: > On Thu, Oct 29, 2020 at 1:04 PM Zi Yan <zi.yan@xxxxxxxx> wrote: >> >> From: Zi Yan <ziy@xxxxxxxxxx> >> >> In isolate_migratepages_block, when cc->alloc_contig is true, we are >> able to isolate compound pages, nr_migratepages and nr_isolated did not >> count compound pages correctly, causing us to isolate more pages than we >> thought. Use thp_nr_pages to count pages. Otherwise, we might be trapped >> in too_many_isolated while loop, since the actual isolated pages can go >> up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32, > > Is it that easy to run into? 16384 doesn't seem like too many pages, just 64MB. I hit this when I was running oom01 from ltp to test my PUD THP patchset, which allocates PUD THPs from CMA regions and splits them into PMD THPs due to memory pressure. I am not sure if it is common that in the upstream kernel PMD THPs will be allocated in CMA regions due to allocation fallback. > >> since we stop isolation after cc->nr_migratepages reaches to >> COMPACT_CLUSTER_MAX. >> >> In addition, after we fix the issue above, cc->nr_migratepages could >> never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated, >> thus page isolation could not stop as we intended. Change the isolation >> stop condition to >=. > > The fix looks sane to me. Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> Thanks. > > Shall you add Fixes tag to commit > 1da2f328fa643bd72197dfed0c655148af31e4eb? And may cc stable. Sure. Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) stable cc’ed. > >> >> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx> >> --- >> mm/compaction.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index ee1f8439369e..0683a4999581 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, >> >> isolate_success: >> list_add(&page->lru, &cc->migratepages); >> - cc->nr_migratepages++; >> - nr_isolated++; >> + cc->nr_migratepages += thp_nr_pages(page); >> + nr_isolated += thp_nr_pages(page); >> >> /* >> * Avoid isolating too much unless this block is being >> @@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, >> * or a lock is contended. For contention, isolate quickly to >> * potentially remove one source of contention. >> */ >> - if (cc->nr_migratepages == COMPACT_CLUSTER_MAX && >> + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX && >> !cc->rescan && !cc->contended) { >> ++low_pfn; >> break; >> @@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, >> if (!pfn) >> break; >> >> - if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) >> + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) >> break; >> } >> >> -- >> 2.28.0 >> >> — Best Regards, Yan Zi
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