From: Sargun Dhillon <sargun@sargun.me>
To: Jeff Layton <jlayton@kernel.org>
Cc: Amir Goldstein <amir73il@gmail.com>,
Miklos Szeredi <miklos@szeredi.hu>,
Vivek Goyal <vgoyal@redhat.com>,
overlayfs <linux-unionfs@vger.kernel.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>, NeilBrown <neilb@suse.com>,
Jan Kara <jack@suse.cz>
Subject: Re: [RFC PATCH 0/2] errseq+overlayfs: accomodate the volatile upper layer use-case
Date: Sun, 13 Dec 2020 20:31:41 +0000 [thread overview]
Message-ID: <20201213203140.GC8562@ircssh-2.c.rugged-nimbus-611.internal> (raw)
In-Reply-To: <20201213132713.66864-1-jlayton@kernel.org>
On Sun, Dec 13, 2020 at 08:27:11AM -0500, Jeff Layton wrote:
> What about this as an alternate approach to the problem that Sargun has
> been working on? I have some minor concerns about the complexity of
> managing a stateful object across two different words. That can be
> done, but I think this may be simpler.
>
> This set steals an extra flag bit from the errseq_t counter so that we
> have two flags: one indicating whether to increment the counter at set
> time, and another to indicate whether the error has been reported to
> userland.
>
This approach works, and I believe you suggested it early on, but I was unsure
whether it was okay to use another bit for state information.
> This should give you the semantics you want in the syncfs case, no? If
> this does look like it's a suitable approach, then I'll plan to clean up
> the comments and docs.
>
From a raw semantics perspective, this looks correct, and it looks like we could
stash it as well for later reference (there's no going backwards, and....well,
2**19 errors is unlikely.). We do ~10s of overlayfs mounts / sec at peak,
but even then we usually see a single disk error on a machine before it fails,
I'm not sure if in the field people get more churn out of the errseq than that.
> I have a vague feeling that this might help us eventually kill the
> AS_EIO and AS_ENOSPC bits too, but that would require a bit more work to
> plumb in "since" samples at appropriate places.
>
> Jeff Layton (2):
> errseq: split the SEEN flag into two new flags
> overlayfs: propagate errors from upper to overlay sb in sync_fs
>
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/super.c | 14 +++++++--
> include/linux/errseq.h | 2 ++
> lib/errseq.c | 64 +++++++++++++++++++++++++++++++++-------
> 4 files changed, 67 insertions(+), 14 deletions(-)
>
> --
> 2.29.2
>
prev parent reply other threads:[~2020-12-13 20:32 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-13 13:27 [RFC PATCH 0/2] errseq+overlayfs: accomodate the volatile upper layer use-case Jeff Layton
2020-12-13 13:27 ` [RFC PATCH 1/2] errseq: split the SEEN flag into two new flags Jeff Layton
2020-12-13 23:35 ` NeilBrown
2020-12-14 13:37 ` Jeffrey Layton
2020-12-14 22:00 ` NeilBrown
2020-12-14 23:32 ` Jeff Layton
2020-12-13 13:27 ` [RFC PATCH 2/2] overlayfs: propagate errors from upper to overlay sb in sync_fs Jeff Layton
2020-12-14 21:38 ` Vivek Goyal
2020-12-14 22:04 ` Sargun Dhillon
2020-12-14 23:01 ` Vivek Goyal
2020-12-14 23:53 ` Jeff Layton
2020-12-15 13:16 ` Jeff Layton
2020-12-15 14:59 ` Vivek Goyal
2020-12-15 15:23 ` Jeff Layton
2020-12-15 15:39 ` Vivek Goyal
2020-12-15 15:06 ` Vivek Goyal
2020-12-17 19:28 ` Sargun Dhillon
2020-12-13 20:31 ` Sargun Dhillon [this message]
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