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Message-ID: <20250316232421.1642758-1-mjguzik@gmail.com>
Date: Mon, 17 Mar 2025 00:24:21 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
jack@...e.cz,
linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] fs: use wq_has_sleeper() in end_dir_add()
The routine is used a lot, while the wakeup almost never has anyone to
deal with.
wake_up_all() takes an irq-protected spinlock, wq_has_sleeper() "only"
contains a full fence -- not free by any means, but still cheaper.
Sample result tracing waiters using a custom probe during -j 20 kernel
build (0 - no waiters, 1 - waiters):
@[
wakeprobe+5
__wake_up_common+63
__wake_up+54
__d_add+234
d_splice_alias+146
ext4_lookup+439
path_openat+1746
do_filp_open+195
do_sys_openat2+153
__x64_sys_openat+86
do_syscall_64+82
entry_SYSCALL_64_after_hwframe+118
]:
[0, 1) 13999 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, ...) 1 | |
So that 14000 calls in total from this backtrace, where only one time
had a waiter.
Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
fs/dcache.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index df8833fe9986..bd5aa136153a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2497,7 +2497,8 @@ static inline void end_dir_add(struct inode *dir, unsigned int n,
{
smp_store_release(&dir->i_dir_seq, n + 2);
preempt_enable_nested();
- wake_up_all(d_wait);
+ if (wq_has_sleeper(d_wait))
+ wake_up_all(d_wait);
}
static void d_wait_lookup(struct dentry *dentry)
--
2.43.0
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