On Wed, Jun 03, 2015 at 11:14:05AM +0200, Vlastimil Babka wrote: > On 04/29/2015 12:44 AM, Kirill A. Shutemov wrote: > >>> > >>> I wrote this to fix bug I originally attributed to refcounting patchset, > >>> but Sasha triggered the same bug on -next without the patchset applied: > >>> > >>> http://lkml.kernel.org/g/553EB993.7030401@xxxxxxxxxx > >> > >> Well why the heck didn't the changelog tell us this?!?!? > > > > Sasha reported bug in -next after I sent the patch. > > > >> > >>> Now I think it's related to changing of PageLRU() behaviour on tail page > >>> by my page flags patchset. > >> > >> So this patch is a bugfix against one of > >> > >> page-flags-trivial-cleanup-for-pagetrans-helpers.patch > >> page-flags-introduce-page-flags-policies-wrt-compound-pages.patch > >> page-flags-define-pg_locked-behavior-on-compound-pages.patch > >> page-flags-define-behavior-of-fs-io-related-flags-on-compound-pages.patch > >> page-flags-define-behavior-of-lru-related-flags-on-compound-pages.patch > > > > ^^^ this one is fault, I think. > > So this patch is now: > http://www.ozlabs.org/~akpm/mmotm/broken-out/page-flags-define-behavior-of-lru-related-flags-on-compound-pages-fix.patch > > I've found a non-fatal but misleading issues. > > First, the "will fail to detect hugetlb pages in this case" part of the > changelog, and mention of hugetlbfs in the comment is AFAIK moot. > There's a PageLRU() check preceding the compound check, so hugetlbfs > pages (which are not PageLRU() AFAIK) are already skipped at that point. > I want to improve that in another series, but that's out of scope here. > > Second, compound_order(page) returns 0 for a tail page, so the ALIGN() > trick that's supposed to properly advance pfn from a tail page is > useless. We could grab a head page, but stumbling on a THP tail page > should be very rare so it's not worth the trouble - just remove the ALIGN. > > From: Vlastimil Babka <vbabka@xxxxxxx> > Date: Wed, 3 Jun 2015 11:03:37 +0200 > Subject: [PATCH] page-flags-define-behavior-of-lru-related-flags-on-compound-pages-fix-fix > > Mentioning hugetlbfs is misleading, because PageLRU() checks skip over hugetlb pages. > The ALIGN() parts are useless, because compound_order(page) returns 0 for tail pages. ACK. > > --- > mm/compaction.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 6ef2fdf..16e1b57 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -733,9 +733,12 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > * if PageLRU is set) but the lock is not necessarily taken > * here and it is wasteful to take it just to check transhuge. > * Check PageCompound without lock and skip the whole pageblock > - * if it's either a transhuge or hugetlbfs page, as calling > - * compound_order() without preventing THP from splitting the > - * page underneath us may return surprising results. > + * if it's a transhuge page, as calling compound_order() > + * without preventing THP from splitting the page underneath us > + * may return surprising results. > + * If we happen to check a THP tail page, compound_order() > + * returns 0. It should be rare enough to not bother with > + * using compound_head() in that case. > */ > if (PageCompound(page)) { > int nr; > @@ -743,7 +746,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > nr = 1 << compound_order(page); > else > nr = pageblock_nr_pages; > - low_pfn = ALIGN(low_pfn + 1, nr) - 1; > + low_pfn += nr - 1; > continue; > } > > @@ -768,7 +771,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > continue; > if (PageCompound(page)) { > int nr = 1 << compound_order(page); > - low_pfn = ALIGN(low_pfn + 1, nr) - 1; > + low_pfn += nr - 1; > continue; > } > } > -- > 2.1.4 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>