Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH v7 0/2] tmpfs: inode: Reduce risk of inum overflow
@ 2020-07-13 17:28 Chris Down
  2020-07-13 17:28 ` [PATCH v7 1/2] tmpfs: Per-superblock i_ino support Chris Down
  2020-07-13 17:28 ` [PATCH v7 2/2] tmpfs: Support 64-bit inums per-sb Chris Down
  0 siblings, 2 replies; 8+ messages in thread
From: Chris Down @ 2020-07-13 17:28 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Hugh Dickins, Al Viro, Matthew Wilcox, Amir Goldstein,
	Jeff Layton, Johannes Weiner, Tejun Heo, linux-mm, linux-fsdevel,
	linux-kernel, kernel-team

In Facebook production we are seeing heavy i_ino wraparounds on tmpfs.
On affected tiers, in excess of 10% of hosts show multiple files with
different content and the same inode number, with some servers even
having as many as 150 duplicated inode numbers with differing file
content.

This causes actual, tangible problems in production. For example, we
have complaints from those working on remote caches that their
application is reporting cache corruptions because it uses (device,
inodenum) to establish the identity of a particular cache object, but
because it's not unique any more, the application refuses to continue
and reports cache corruption. Even worse, sometimes applications may not
even detect the corruption but may continue anyway, causing phantom and
hard to debug behaviour.

In general, userspace applications expect that (device, inodenum) should
be enough to be uniquely point to one inode, which seems fair enough.
One might also need to check the generation, but in this case:

1. That's not currently exposed to userspace
   (ioctl(...FS_IOC_GETVERSION...) returns ENOTTY on tmpfs);
2. Even with generation, there shouldn't be two live inodes with the
   same inode number on one device.

In order to mitigate this, we take a two-pronged approach:

1. Moving inum generation from being global to per-sb for tmpfs. This
   itself allows some reduction in i_ino churn. This works on both 64-
   and 32- bit machines.
2. Adding inode{64,32} for tmpfs. This fix is supported on machines with
   64-bit ino_t only: we allow users to mount tmpfs with a new inode64
   option that uses the full width of ino_t, or CONFIG_TMPFS_INODE64.

You can see how this compares to previous related patches which didn't
implement this per-superblock:

- https://patchwork.kernel.org/patch/11254001/
- https://patchwork.kernel.org/patch/11023915/

Changes since v6:

- Fix misalignment in percpu batching, thanks Matthew.

Chris Down (2):
  tmpfs: Per-superblock i_ino support
  tmpfs: Support 64-bit inums per-sb

 Documentation/filesystems/tmpfs.rst |  11 +++
 fs/Kconfig                          |  15 ++++
 include/linux/fs.h                  |  15 ++++
 include/linux/shmem_fs.h            |   3 +
 mm/shmem.c                          | 127 ++++++++++++++++++++++++++--
 5 files changed, 166 insertions(+), 5 deletions(-)

-- 
2.27.0



^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, back to index

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-13 17:28 [PATCH v7 0/2] tmpfs: inode: Reduce risk of inum overflow Chris Down
2020-07-13 17:28 ` [PATCH v7 1/2] tmpfs: Per-superblock i_ino support Chris Down
2020-08-01 19:22   ` Hugh Dickins
2020-07-13 17:28 ` [PATCH v7 2/2] tmpfs: Support 64-bit inums per-sb Chris Down
2020-08-01 20:41   ` Hugh Dickins
2020-08-02  2:37     ` [PATCH mmotm] tmpfs: support 64-bit inums per-sb fix Hugh Dickins
2020-08-02  3:05       ` Randy Dunlap
2020-08-02  5:25         ` Hugh Dickins

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git