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References: <20220224161705.1041788-1-amir73il@gmail.com> <BB7DEB92-1E3D-4BF5-A723-650C2B95877D@oracle.com>
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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Thu, 24 Feb 2022 23:39:30 +0200
Message-ID: <CAOQ4uxgUEn0MpBYH8YU3paeJ5r0n545FuWmzb_yLEyoa1VkVtw@mail.gmail.com>
Subject: Re: [PATCH v2] nfsd: more robust allocation failure handling in nfsd_file_cache_init
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Thu, Feb 24, 2022 at 10:41 PM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
> Hi Amir-
>
> > On Feb 24, 2022, at 11:17 AM, Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > The nfsd file cache table can be pretty large and its allocation
> > may require as many as 80 contigious pages.
> >
> > Employ the same fix that was employed for similar issue that was
> > reported for the reply cache hash table allocation several years ago
> > by commit 8f97514b423a ("nfsd: more robust allocation failure handling
> > in nfsd_reply_cache_init").
> >
> > Fixes: 65294c1f2c5e ("nfsd: add a new struct file caching facility to nfsd")
> > Link: https://lore.kernel.org/linux-nfs/e3cdaeec85a6cfec980e87fc294327c0381c1778.camel@kernel.org/
> > Suggested-by: Jeff Layton <jlayton@kernel.org>
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> >
> > Since v1:
> > - Use kvcalloc()
> > - Use kvfree()
> >
> > fs/nfsd/filecache.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
>
> v2 passes some simple testing, so I've applied it to NFSD for-next.
> It should get 0-day and merge testing and is available for others
> to try out.
>
> I don't have anything that exercises low memory scenarios, though.
> Do you have anything like this to try?

Well, it is not low memory really it's fragmented memory.
I would try setting:

CONFIG_FAIL_PAGE_ALLOC=y

echo 5 > /sys/kernel/debug/fail_page_alloc/min-order
echo 100 > /sys/kernel/debug/fail_page_alloc/probability

and starting (or restarting) nfsd.
hoping that other large page allocations won't get in the way.

I gave it a shot, but couldn't figure out why nfsd4_files slab
is still there after stopping nfs-server service, meaning that
nfsd_file_cache_shutdown() was not called - I must be missing
something. I may play with this some more tomorrow.

Thanks,
Amir.