Re: [PATCH] pagemap: fix wrong KPF_THP on slab pages
From: Fengguang Wu <hidden>
Date: 2012-09-26 02:48:29
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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:quoted
On Tue, 25 Sep 2012, Naoya Horiguchi wrote:quoted
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 <redacted>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 <redacted> 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/
quoted hunk ↗ jump to hunk
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 <redacted> --- 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>