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. -- Michal Hocko SUSE Labs
