On Mon, Nov 2, 2020 at 5:03 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > On 10/30/20 7:55 PM, Yang Shi wrote: > > On Fri, Oct 30, 2020 at 11:39 AM Zi Yan <ziy@xxxxxxxxxx> wrote: > >> > >> 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. > > > > Thanks. Actually I'm wondering what kind of movable page could be > > compound. Any real examples? > > Looks like there's currently none. Compaction also wouldn't work properly with > movable pages with order>0 as the free page scanner looks for order-0 pages > only. But it won't hurt to use compound_nr() anyway. Thanks, yes this is what I thought otherwise we have troubles in migration path too. > > >> > >> — > >> Best Regards, > >> Yan Zi > > >
