On 30 Oct 2020, at 9:36, Michal Hocko 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? __PageMovable, non-lru movable pages, can be compound and thp_nr_page cannot be used for it, since when THP is off, thp_nr_page will return the wrong number. I got confused by its name, sorry. But __PageMovable is irrelevant to this patch, since we are using __isolate_lru_page to isolate pages. non-lru __PageMovable should not appear after isolate_succes. thp_nr_pages can be used here. — Best Regards, Yan Zi
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