On Tue, Jun 18, 2013 at 02:47:04PM -0400, Joern Engel wrote: > When moving a program from mmap'ing small pages to mmap'ing huge pages, > a remarkable drop in rss ensues. For some reason hugepages were never > accounted for in rss, which in my book is a clear bug. Sadly this bug > has been present in hugetlbfs since it was merged back in 2002. There > is every chance existing programs depend on hugepages not being counted > as rss. > > I think the correct solution is to fix the bug and wait for someone to > complain. It is just as likely that noone cares - as evidenced by the > fact that noone seems to have noticed for ten years. > > Signed-off-by: Joern Engel <joern@xxxxxxxxx> > --- > mm/hugetlb.c | 4 ++++ > 1 file changed, 4 insertions(+) > Hi, This patch has caused a few warnings for me today when it was integrated into linux-next. The libhugetlbfs test suite gave me: [ 94.320661] BUG: Bad rss-counter state mm:ffff880119461040 idx:1 val:-512 [ 94.330346] BUG: Bad rss-counter state mm:ffff880119460680 idx:1 val:-2560 [ 94.341746] BUG: Bad rss-counter state mm:ffff880119460d00 idx:1 val:-512 [ 94.347518] BUG: Bad rss-counter state mm:ffff880119460d00 idx:1 val:-512 [ 94.415203] BUG: Bad rss-counter state mm:ffff8801194f9040 idx:1 val:-1024 [ ...] I think I've found the cause; MAP_SHARED mappings. alloc_huge_page and __unmap_hugepage_range are called for shared pages. Also, __unmap_hugepage_range is called more times than alloc_huge_page (which makes sense as multiple views of a shared mapping are unmapped) leading to negative counter values. Excluding VM_SHARED VMAs from the counter increment/decrement stopped the warnings for me. Although this may not be the best way to address the issue. Cheers, -- Steve -- 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>