netdev - Re: [PATCH RFC 00/30] Overhaul NFSD filecache

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Date:   Fri, 24 Jun 2022 01:51:22 +0800
From:   Wang Yugui <wangyugui@...-tech.com>
To:     Chuck Lever III <chuck.lever@...cle.com>
Cc:     Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "tgraf@...g.ch" <tgraf@...g.ch>, Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH RFC 00/30] Overhaul NFSD filecache

Hi,

> > On Jun 23, 2022, at 5:02 AM, Wang Yugui <wangyugui@...-tech.com> wrote:
> > 
> > Hi,
> > 
> >>> On Jun 22, 2022, at 3:04 PM, Chuck Lever III <chuck.lever@...cle.com> wrote:
> >>>> On Jun 22, 2022, at 2:36 PM, Wang Yugui <wangyugui@...-tech.com> wrote:
> >>>> 
> >>>> Hi,
> >>>> 
> >>>> fstests generic/531 triggered a panic on kernel 5.19.0-rc3 with this
> >>>> patchset.
> >>> 
> >>> As I mention in the cover letter, I haven't tried running generic/531
> >>> yet -- no claim at all that this is finished work and that #386 has
> >>> been fixed at this point. I'm merely interested in comments on the
> >>> general approach.
> >>> 
> >>> 
> >>>> [ 405.478056] BUG: kernel NULL pointer dereference, address: 0000000000000049
> >>> 
> >>> The "RIP: " tells the location of the crash. Notice that the call
> >>> trace here does not include that information. From your attachment:
> >>> 
> >>> [ 405.518022] RIP: 0010:nfsd_do_file_acquire+0x4e1/0xb80 [nfsd]
> >>> 
> >>> To match that to a line of source code:
> >>> 
> >>> [cel@...et ~]$ cd src/linux/linux/
> >>> [cel@...et linux]$ scripts/faddr2line ../obj/manet/fs/nfsd/filecache.o nfsd_do_file_acquire+0x4e1
> >>> nfsd_do_file_acquire+0x4e1/0xfc0:
> >>> rht_bucket_insert at /home/cel/src/linux/linux/include/linux/rhashtable.h:303
> >>> (inlined by) __rhashtable_insert_fast at /home/cel/src/linux/linux/include/linux/rhashtable.h:718
> >>> (inlined by) rhashtable_lookup_get_insert_key at /home/cel/src/linux/linux/include/linux/rhashtable.h:982
> >>> (inlined by) nfsd_file_insert at /home/cel/src/linux/linux/fs/nfsd/filecache.c:1031
> >>> (inlined by) nfsd_do_file_acquire at /home/cel/src/linux/linux/fs/nfsd/filecache.c:1089
> >>> [cel@...et linux]$
> >>> 
> >>> This is an example, I'm sure my compiled objects don't match yours.
> >>> 
> >>> And, now that I've added observability, you should be able to do:
> >>> 
> >>> # watch cat /proc/fs/nfsd/filecache
> >>> 
> >>> to see how many items are in the hash and LRU list while the test
> >>> is running.
> >>> 
> >>> 
> >>>> [ 405.608016] Call Trace:
> >>>> [ 405.608016] <TASK>
> >>>> [ 405.613020] nfs4_get_vfs_file+0x325/0x410 [nfsd]
> >>>> [ 405.618018] nfsd4_process_open2+0x4ba/0x16d0 [nfsd]
> >>>> [ 405.623016] ? inode_get_bytes+0x38/0x40
> >>>> [ 405.623016] ? nfsd_permission+0x97/0xf0 [nfsd]
> >>>> [ 405.628022] ? fh_verify+0x1cc/0x6f0 [nfsd]
> >>>> [ 405.633025] nfsd4_open+0x640/0xb30 [nfsd]
> >>>> [ 405.638025] nfsd4_proc_compound+0x3bd/0x710 [nfsd]
> >>>> [ 405.643017] nfsd_dispatch+0x143/0x270 [nfsd]
> >>>> [ 405.648019] svc_process_common+0x3bf/0x5b0 [sunrpc]
> >> 
> >> I was able to trigger something that looks very much like this crash.
> >> If you remove this line from fs/nfsd/filecache.c:
> >> 
> >> 	.max_size		= 131072, /* buckets */
> >> 
> >> things get a lot more stable for generic/531.
> >> 
> >> I'm looking into the issue now.
> > 
> > Yes. When '.max_size = 131072' is removed, fstests generic/531 passed.
> 
> Great! Are you comfortable with this general approach for bug #386?

It seems a good result for #386.

fstests generic/531(file-max: 1M) performance result:
base(5.19.0-rc3, 12 bits hash, serialized nfsd_file_gc): 222s
this patchset(.min_size=4096): 59s
so, a good improvement for #386.

It seems a good(acceptable) result for #387 too.
the period of 'text busy(exec directly from the back-end of nfs-server)'
is about 4s.

Best Regards
Wang Yugui (wangyugui@...-tech.com)
2022/06/24