From: Hugh Dickins <hughd@google.com>
To: "J. R. Okajima" <hooanon05g@gmail.com>
Cc: Hugh Dickins <hughd@google.com>,
"zhengbin (A)" <zhengbin13@huawei.com>,
Matthew Wilcox <willy@infradead.org>,
viro@zeniv.linux.org.uk, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, houtao1@huawei.com,
yi.zhang@huawei.com
Subject: Re: [PATCH] tmpfs: use ida to get inode number
Date: Thu, 21 Nov 2019 12:07:43 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.11.1911211154090.1697@eggly.anvils> (raw)
In-Reply-To: <32188.1574336426@jrobl>
On Thu, 21 Nov 2019, J. R. Okajima wrote:
> Hugh Dickins:
> > Internally (in Google) we do rely on good tmpfs inode numbers more
> > than on those of other get_next_ino() filesystems, and carry a patch
> > to mm/shmem.c for it to use 64-bit inode numbers (and separate inode
> > number space for each superblock) - essentially,
> >
> > =09ino =3D sbinfo->next_ino++;
> > =09/* Avoid 0 in the low 32 bits: might appear deleted */
> > =09if (unlikely((unsigned int)ino =3D=3D 0))
> > =09=09ino =3D sbinfo->next_ino++;
>
> I agree with that "per superblock inum space", but I don't see your
> point. How can you manage it fully? I mean how can you decide whether
> the new inum is in use or not?
> For example,
> - you create a file which is assigned inum#10.
> - you or other people create and unlink over and over on the same tmpfs.
> - then sbinfo->next_ino will become zero, skipped, ok.
> - and then it will be 10.
> I don't think you want to share the same inum by two inodes.
64 bits. I haven't done the arithmetic to work out the amusing number,
but zhengbin mentioned the script taking 10 days to duplicate an inode
number in 32 bits, so: a larger number of years than I need to care about.
>
> Moreover, SysV SHM uses tmpfs and shmget(2) overwrite inum internally.
> It will be another seed of a similar problem.
I was totally ignorant of that peculiarity in ipc/shm.c, thanks for
alerting me to it. But it doesn't affect what we're doing in tmpfs,
and apparently suits the users of SysV SHM: I don't see any need to
worry about it.
Hugh
next prev parent reply other threads:[~2019-11-21 20:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-20 14:23 [PATCH] tmpfs: use ida to get inode number zhengbin
2019-11-20 15:45 ` Matthew Wilcox
2019-11-21 2:36 ` zhengbin (A)
2019-11-21 4:52 ` Hugh Dickins
2019-11-21 6:45 ` zhengbin (A)
2019-11-21 19:53 ` Hugh Dickins
2019-11-22 1:23 ` zhengbin (A)
2019-11-22 22:13 ` Matthew Wilcox
2019-11-23 2:16 ` zhengbin (A)
2019-11-23 2:33 ` Matthew Wilcox
2019-11-23 4:54 ` Al Viro
2019-12-01 8:44 ` zhengbin (A)
2019-11-21 11:40 ` J. R. Okajima
2019-11-21 20:07 ` Hugh Dickins [this message]
2019-11-21 4:31 ` Al Viro
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