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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Waiman Long <longman@redhat.com>
Subject: [PATCH RFC 4/8] fsnotify: stop walking child dentries if remaining tail is negative
Date: Fri, 08 May 2020 15:23:23 +0300	[thread overview]
Message-ID: <158894060308.200862.2000400345829882905.stgit@buzz> (raw)
In-Reply-To: <158893941613.200862.4094521350329937435.stgit@buzz>

When notification starts/stops listening events from inode's children it
have to update dentry->d_flags of all positive child dentries. Scanning
may took a long time if directory has a lot of negative child dentries.

This is main beneficiary of sweeping cached negative dentries to the end.

Before patch:

nr_dentry = 24172597	24.2M
nr_buckets = 8388608	2.9 avg
nr_unused = 24158110	99.9%
nr_negative = 24142810	99.9%

inotify time: 0.507182 seconds

After patch:

nr_dentry = 24562747    24.6M
nr_buckets = 8388608    2.9 avg
nr_unused = 24548714    99.9%
nr_negative = 24543867  99.9%

inotify time: 0.000010 seconds

Negative dentries no longer slow down inotify op at parent directory.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 fs/notify/fsnotify.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 72d332ce8e12..072974302950 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -127,8 +127,12 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 		 * original inode) */
 		spin_lock(&alias->d_lock);
 		list_for_each_entry(child, &alias->d_subdirs, d_child) {
-			if (!child->d_inode)
+			if (!child->d_inode) {
+				/* all remaining children are negative */
+				if (d_is_tail_negative(child))
+					break;
 				continue;
+			}
 
 			spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
 			if (watched)


  parent reply	other threads:[~2020-05-08 12:23 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-08 12:23 [PATCH RFC 0/8] dcache: increase poison resistance Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state Konstantin Khlebnikov
2020-05-08 14:49   ` Waiman Long
2020-05-08 16:16     ` Konstantin Khlebnikov
2020-05-08 19:05       ` Waiman Long
2020-05-08 19:38         ` Konstantin Khlebnikov
2020-05-08 20:00           ` Waiman Long
2020-05-08 20:03             ` Matthew Wilcox
2020-05-08 12:23 ` [PATCH RFC 2/8] selftests: add stress testing tool for dcache Konstantin Khlebnikov
2020-05-13  1:52   ` Dave Chinner
2020-05-08 12:23 ` [PATCH RFC 3/8] dcache: sweep cached negative dentries to the end of list of siblings Konstantin Khlebnikov
2020-05-08 19:38   ` Waiman Long
2020-05-08 12:23 ` Konstantin Khlebnikov [this message]
2020-05-08 12:23 ` [PATCH RFC 5/8] dcache: add action D_WALK_SKIP_SIBLINGS to d_walk() Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 6/8] dcache: stop walking siblings if remaining dentries all negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 7/8] dcache: push releasing dentry lock into sweep_negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 8/8] dcache: prevent flooding with negative dentries Konstantin Khlebnikov
2020-05-08 14:56   ` Matthew Wilcox
2020-05-08 16:29     ` Konstantin Khlebnikov
2020-05-08 21:07   ` Waiman Long
2020-12-09 23:01 ` [PATCH RFC 0/8] dcache: increase poison resistance Junxiao Bi
     [not found]   ` <CALYGNiN2F8gcKX+2nKOi1tapquJWfyzUkajWxTqgd9xvd7u1AA@mail.gmail.com>
2020-12-13 18:49     ` Junxiao Bi
     [not found]       ` <CALYGNiM8Fp=ZV8S6c2L50ne1cGhE30PrT-C=4nfershvfAgP+Q@mail.gmail.com>
2020-12-14 23:10         ` Junxiao Bi
2020-12-16 18:46           ` Junxiao Bi

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