On 30 Oct 2020, at 10:49, Michal Hocko wrote: > On Fri 30-10-20 10:35:43, Zi Yan wrote: >> 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. > > OK, this matches my understanding. Good we are on the same page. > >> 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. > > But this is still not clear to me. __PageMovable pages are isolated by > isolate_movable_page and then jump to isolate_succes. Does that somehow > changes the nature of the page being compound or tat thp_nr_page would > start working on those pages. Ah, I missed that part of the code. If __PageMovable can reach the code, we should use compound_nr instead. Will send v2 to fix it. Thanks. — Best Regards, Yan Zi
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