On Tue, Sep 25, 2012 at 10:06:08PM -0400, Naoya Horiguchi wrote: > On Tue, Sep 25, 2012 at 05:20:48PM -0700, David Rientjes wrote: > > On Tue, 25 Sep 2012, Naoya Horiguchi wrote: > > > > > KPF_THP can be set on non-huge compound pages like slab pages, because > > > PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug > > > and breaks user space applications which look for thp via /proc/kpageflags. > > > Currently thp is constructed only on anonymous pages, so this patch makes > > > KPF_THP be set when both of PageAnon and PageTransCompound are true. > > > > > > Changelog in v2: > > > - add a comment in code > > > > > > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > > > > Wouldn't PageTransCompound(page) && !PageHuge(page) && !PageSlab(page) be > > better for a future extension of thp support? > > Yes, this saves us an additional change when thp starts handling pagecaches. > Andrew, can you replace the previous version in -mm tree with new one below? > > Thanks, > Naoya > --- > From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Date: Tue, 25 Sep 2012 21:30:25 -0400 > Subject: [PATCH v3] kpageflags: fix wrong KPF_THP on slab pages > > KPF_THP can be set on non-huge compound pages like slab pages, because > PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug s/sees/checks/ > and breaks user space applications which look for thp via /proc/kpageflags. > This patch rules out setting KPF_THP wrongly by additional PageSlab check. > > Changelog in v3: > - check PageSlab instead of PageAnon > - fix patch subject > > Changelog in v2: > - add a comment in code > > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > --- > fs/proc/page.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/page.c b/fs/proc/page.c > index 7fcd0d6..e36d1f3 100644 > --- a/fs/proc/page.c > +++ b/fs/proc/page.c > @@ -115,7 +115,12 @@ u64 stable_page_flags(struct page *page) > u |= 1 << KPF_COMPOUND_TAIL; > if (PageHuge(page)) > u |= 1 << KPF_HUGE; > - else if (PageTransCompound(page)) > + /* > + * PageTransCompound can be true for slab pages because it just sees s/sees/checks/ > + * PG_head/PG_head, so we need to check PageSlab to make sure the given PG_head/PG_head should be PG_head/PG_tail. > + * page is a thp, not a non-huge compound page. > + */ > + else if (PageTransCompound(page) && !PageSlab(page)) > u |= 1 << KPF_THP; Good catch! Will this report THP for the various drivers that do __GFP_COMP page allocations? Thanks, Fengguang -- 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>