Kirill A. Shutemov c761471b58 mm: avoid tail page refcounting on non-THP compound pages ... Reintroduce 8d63d99a5d ("mm: avoid tail page refcounting on non-THP compound pages") after removing bogus VM_BUG_ON_PAGE() in put_unrefcounted_compound_page(). THP uses tail page refcounting to be able to split huge pages at any time. Tail page refcounting is not needed for other users of compound pages and it's harmful because of overhead. We try to exclude non-THP pages from tail page refcounting using __compound_tail_refcounted() check. It excludes most common non-THP compound pages: SL*B and hugetlb, but it doesn't catch rest of __GFP_COMP users -- drivers. And it's not only about overhead. Drivers might want to use compound pages to get refcounting semantics suitable for mapping high-order pages to userspace. But tail page refcounting breaks it. Tail page refcounting uses ->_mapcount in tail pages to store GUP pins on them. It means GUP pins would affect page_mapcount() for tail pages. It's not a problem for THP, because it never maps tail pages. But unlike THP, drivers map parts of compound pages with PTEs and it makes page_mapcount() be called for tail pages. In particular, GUP pins would shift PSS up and affect /proc/kpagecount for such pages. But, I'm not aware about anything which can lead to crash or other serious misbehaviour. Since currently all THP pages are anonymous and all drivers pages are not, we can fix the __compound_tail_refcounted() check by requiring PageAnon() to enable tail page refcounting. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Borislav Petkov <bp@alien8.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2015-06-24 17:49:42 -07:00
..
acpi	Merge branch 'acpi-cca'	2015-06-19 01:17:35 +02:00
asm-generic	PCI changes for the v4.2 merge window:	2015-06-23 13:41:24 -07:00
clocksource
crypto	crypto: rng - Do not free default RNG when it becomes unused	2015-06-22 15:49:18 +08:00
drm
dt-bindings	mfd: arizona: Add convience defines for micd_rate/micd_bias_starttime	2015-06-22 12:25:22 +01:00
keys
kvm
linux	mm: avoid tail page refcounting on non-THP compound pages	2015-06-24 17:49:42 -07:00
math-emu
media
memory
misc	cxl: Add AFU virtual PHB and kernel API	2015-06-03 13:27:20 +10:00
net	Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6	2015-06-22 21:04:48 -07:00
pcmcia
ras
rdma	IB/mad: Add final OPA MAD processing	2015-06-12 14:49:18 -04:00
rxrpc
scsi	SCSI misc on 20150622	2015-06-23 15:55:44 -07:00
soc
sound	ALSA: hda - Re-add the lost fake mute support	2015-06-11 11:55:48 +02:00
target	SCSI misc on 20150622	2015-06-23 15:55:44 -07:00
trace	SCSI misc on 20150622	2015-06-23 15:55:44 -07:00
uapi	The bulk of the changes here is for x86. And for once it's not	2015-06-24 09:36:49 -07:00
video	video: fbdev: tdfxfb: use arch_phys_wc_add() and ioremap_wc()	2015-06-03 12:41:52 +03:00
xen	xen/events: don't bind non-percpu VIRQs with percpu chip	2015-05-19 19:55:36 +01:00
Kbuild