linux/include
Hugh Dickins 9b15b817f3 swap: fix shmem swapping when more than 8 areas
Minchan Kim reports that when a system has many swap areas, and tmpfs
swaps out to the ninth or more, shmem_getpage_gfp()'s attempts to read
back the page cannot locate it, and the read fails with -ENOMEM.

Whoops.  Yes, I blindly followed read_swap_header()'s pte_to_swp_entry(
swp_entry_to_pte()) technique for determining maximum usable swap
offset, without stopping to realize that that actually depends upon the
pte swap encoding shifting swap offset to the higher bits and truncating
it there.  Whereas our radix_tree swap encoding leaves offset in the
lower bits: it's swap "type" (that is, index of swap area) that was
truncated.

Fix it by reducing the SWP_TYPE_SHIFT() in swapops.h, and removing the
broken radix_to_swp_entry(swp_to_radix_entry()) from read_swap_header().

This does not reduce the usable size of a swap area any further, it
leaves it as claimed when making the original commit: no change from 3.0
on x86_64, nor on i386 without PAE; but 3.0's 512GB is reduced to 128GB
per swapfile on i386 with PAE.  It's not a change I would have risked
five years ago, but with x86_64 supported for ten years, I believe it's
appropriate now.

Hmm, and what if some architecture implements its swap pte with offset
encoded below type? That would equally break the maximum usable swap
offset check.  Happily, they all follow the same tradition of encoding
offset above type, but I'll prepare a check on that for next.

Reported-and-Reviewed-and-Tested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org [3.1, 3.2, 3.3, 3.4]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-06-15 21:48:14 -07:00
..
acpi ACPI: fix acpi_bus.h build warnings when ACPI is not enabled 2012-06-04 00:29:11 -04:00
asm-generic Merge branches 'sh/urgent', 'sh/core', 'sh/clockevents', 'sh/asm-generic' and 'sh/trivial' into sh-fixes-for-linus 2012-06-13 12:01:33 +09:00
crypto
drm drm: increase DRM_OBJECT_MAX_PROPERTY to 24 2012-06-12 15:36:31 +01:00
keys KEYS: Permit in-place link replacement in keyring list 2012-05-11 10:56:56 +01:00
linux swap: fix shmem swapping when more than 8 areas 2012-06-15 21:48:14 -07:00
math-emu
media [media] patch for Asus My Cinema PS3-100 (1043:48cd) 2012-05-20 16:05:02 -03:00
memory
misc
mtd UBI: amend commentaries WRT dtype 2012-05-20 20:25:59 +03:00
net bonding: Fix corrupted queue_mapping 2012-06-12 15:29:21 -07:00
pcmcia
rdma Merge branches 'core', 'cxgb4', 'ipath', 'iser', 'lockdep', 'mlx4', 'nes', 'ocrdma', 'qib' and 'raw-qp' into for-linus 2012-05-21 09:00:47 -07:00
rxrpc
scsi [SCSI] fcoe, bnx2fc, libfcoe: SW FCoE and bnx2fc use FCoE Syfs 2012-05-23 09:43:13 +01:00
sound ASoC: Last minute updates 2012-05-22 02:58:55 +02:00
target target: Add TFO->put_session() caller for HW fabric session shutdown 2012-06-12 19:33:05 -07:00
trace rcu: Update RCU_FAST_NO_HZ tracing for lazy callbacks 2012-06-06 20:43:27 -07:00
video fbdev updates for 3.5 2012-06-01 16:57:51 -07:00
xen xen: do not map the same GSI twice in PVHVM guests. 2012-05-21 14:11:36 -04:00
Kbuild