On 30 Oct 2020, at 14:33, Yang Shi wrote: > On Fri, Oct 30, 2020 at 6:36 AM Michal Hocko <mhocko@xxxxxxxx> wrote: >> >> On Fri 30-10-20 08:20:50, Zi Yan wrote: >>> On 30 Oct 2020, at 5:43, Michal Hocko wrote: >>> >>>> [Cc Vlastimil] >>>> >>>> On Thu 29-10-20 16:04:35, Zi Yan 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, >>>>> 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 >=. >>>>> >>>>> 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); >>>> >>>> Does thp_nr_pages work for __PageMovable pages? >>> >>> Yes. It is the same as compound_nr() but compiled >>> to 1 when THP is not enabled. >> >> I am sorry but I do not follow. First of all the implementation of the >> two is different and also I was asking about __PageMovable which should >> never be THP IIRC. Can they be compound though? > > I have the same question, can they be compound? If they can be > compound, PageTransHuge() can't tell from THP and compound movable > page, right? Right. I have updated the patch and use compound_nr instead. — Best Regards, Yan Zi
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