From: Al Viro <viro@ZenIV.linux.org.uk>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-fsdevel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Christoph Hellwig <hch@lst.de>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 5/6] fs/dcache: Avoid a try_lock loop in shrink_dentry_list()
Date: Fri, 23 Feb 2018 03:48:27 +0000 [thread overview]
Message-ID: <20180223034827.GY30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180222235025.28662-6-john.ogness@linutronix.de>
On Fri, Feb 23, 2018 at 12:50:24AM +0100, John Ogness wrote:
> - while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
> - parent = lock_parent(dentry);
> - if (dentry->d_lockref.count != 1) {
> - dentry->d_lockref.count--;
> - spin_unlock(&dentry->d_lock);
> - if (parent)
> - spin_unlock(&parent->d_lock);
> - break;
> - }
> - inode = dentry->d_inode; /* can't be NULL */
> - if (unlikely(!spin_trylock(&inode->i_lock))) {
> - spin_unlock(&dentry->d_lock);
> - if (parent)
> - spin_unlock(&parent->d_lock);
> - cpu_relax();
> - continue;
> - }
> - __dentry_kill(dentry);
> - dentry = parent;
> - }
> + while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
> + dentry = dentry_kill(dentry);
Hmm... OK, that's interesting. I agree that it looks similar to dentry_kill()
loop, with one exception - here we are aggressively pruning the branch. None
of the "do we want to retain that sucker" stuff here. It doesn't matter for
most of the callers, with one exception: prune_dcache_sb(). OTOH, there it
just might be the right thing to do anyway - after all, it matters only if
somebody has grabbed and dropped the sucker while we'd been trying to do
lock_parent(). Had we lost the race with their dput(), we would've left
the damn thing alone, and we are called from a memory shrinker, so we'll get
called again if needed.
next prev parent reply other threads:[~2018-02-23 3:48 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 23:50 [PATCH v2 0/6] fs/dcache: avoid trylock loops John Ogness
2018-02-22 23:50 ` [PATCH v2 1/6] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-22 23:50 ` [PATCH v2 2/6] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-22 23:50 ` [PATCH v2 3/6] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-23 2:08 ` Al Viro
2018-02-22 23:50 ` [PATCH v2 4/6] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-23 2:22 ` Al Viro
2018-02-23 3:12 ` Al Viro
2018-02-23 3:16 ` Al Viro
2018-02-23 5:46 ` Al Viro
2018-02-22 23:50 ` [PATCH v2 5/6] fs/dcache: Avoid a try_lock loop in shrink_dentry_list() John Ogness
2018-02-23 3:48 ` Al Viro [this message]
2018-02-22 23:50 ` [PATCH v2 6/6] fs/dcache: Avoid remaining " John Ogness
2018-02-23 3:58 ` Al Viro
2018-02-23 4:08 ` Al Viro
2018-02-23 13:57 ` John Ogness
2018-02-23 15:09 ` Al Viro
2018-02-23 17:42 ` Al Viro
2018-02-23 20:13 ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Al Viro
2018-02-23 21:35 ` Linus Torvalds
2018-02-24 0:22 ` Al Viro
2018-02-25 7:40 ` Al Viro
2018-02-27 5:16 ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) John Ogness
2018-03-12 19:13 ` Al Viro
2018-03-12 20:05 ` Al Viro
2018-03-12 20:33 ` Al Viro
2018-03-13 1:12 ` NeilBrown
2018-04-28 0:10 ` Al Viro
2018-03-12 20:23 ` Eric W. Biederman
2018-03-12 20:39 ` Al Viro
2018-03-12 23:28 ` Eric W. Biederman
2018-03-12 23:52 ` Eric W. Biederman
2018-03-13 0:37 ` Al Viro
2018-03-13 0:50 ` Al Viro
2018-03-13 4:02 ` Eric W. Biederman
2018-03-14 23:20 ` [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots Eric W. Biederman
2018-03-15 22:34 ` Al Viro
2018-03-13 0:36 ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) Al Viro
2018-03-12 22:14 ` Thomas Gleixner
2018-03-13 20:46 ` John Ogness
2018-03-13 21:05 ` John Ogness
2018-03-13 23:59 ` Al Viro
2018-03-14 2:58 ` Matthew Wilcox
2018-03-14 8:18 ` John Ogness
2018-03-02 9:04 ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Sebastian Andrzej Siewior
2018-02-23 0:59 ` [PATCH v2 0/6] fs/dcache: avoid trylock loops Linus Torvalds
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