From: Al Viro <viro@zeniv.linux.org.uk>
To: Gautham Ananthakrishna <gautham.ananthakrishna@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, matthew.wilcox@oracle.com,
khlebnikov@yandex-team.ru
Subject: Re: [PATCH RFC 1/6] dcache: sweep cached negative dentries to the end of list of siblings
Date: Thu, 15 Apr 2021 16:25:05 +0000 [thread overview]
Message-ID: <YHho4TKjqYNmMy6W@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YHZkVlhchiNB9o18@zeniv-ca.linux.org.uk>
On Wed, Apr 14, 2021 at 03:41:10AM +0000, Al Viro wrote:
> > + if (!d_is_tail_negative(dentry)) {
> > + parent = lock_parent(dentry);
> > + if (!parent)
> > + return;
>
> Wait a minute. It's not a good environment for calling lock_parent().
> Who said that dentry won't get freed right under it?
[snip]
FWIW, in that state (dentry->d_lock held) we have
* stable ->d_flags
* stable ->d_count
* stable ->d_inode
IOW, we can bloody well check ->d_count *before* bothering with lock_parent().
It does not get rid of the problems with lifetimes, though. We could
do something along the lines of
rcu_read_lock()
if retain_dentry()
parent = NULL
if that dentry might need to be moved in list
parent = lock_parent()
// if reached __dentry_kill(), d_count() will be -128,
// so the check below will exclude those
if that dentry does need to be moved
move it to the end of list
unlock dentry and parent (if any)
rcu_read_unlock()
return
here, but your other uses of lock_parent() also need attention. And
recursive call of dput() in trim_negative() (#6/6) is really asking
for trouble.
next prev parent reply other threads:[~2021-04-15 16:25 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 13:19 [PATCH RFC 0/6] fix the negative dentres bloating system memory usage Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 1/6] dcache: sweep cached negative dentries to the end of list of siblings Gautham Ananthakrishna
2021-04-14 3:00 ` Al Viro
2021-04-15 16:50 ` Al Viro
2021-04-14 3:41 ` Al Viro
2021-04-15 16:25 ` Al Viro [this message]
2021-01-21 13:19 ` [PATCH RFC 2/6] fsnotify: stop walking child dentries if remaining tail is negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 3/6] dcache: add action D_WALK_SKIP_SIBLINGS to d_walk() Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 4/6] dcache: stop walking siblings if remaining dentries all negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 5/6] dcache: push releasing dentry lock into sweep_negative Gautham Ananthakrishna
2021-01-21 13:19 ` [PATCH RFC 6/6] dcache: prevent flooding with negative dentries Gautham Ananthakrishna
2021-04-14 3:56 ` Al Viro
2021-03-31 14:23 ` [PATCH RFC 0/6] fix the negative dentres bloating system memory usage Matthew Wilcox
2021-04-14 2:40 ` Al Viro
2021-01-21 16:17 [PATCH RFC 1/6] dcache: sweep cached negative dentries to the end of list of siblings kernel test robot
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