linux-kernel - aio: bump i_count instead of using igrab

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100823144755.GP21975@think>
Date:	Mon, 23 Aug 2010 10:47:55 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Jeff Moyer <jmoyer@...hat.com>
Subject: aio: bump i_count instead of using igrab

The aio batching code is using igrab to get an extra reference on the
inode so it can safely batch.  igrab will go ahead and take the global
inode spinlock, which can be a bottleneck on large machines doing lots
of AIO.

In this case, igrab isn't required because we already have a reference
on the file handle.  It is safe to just bump the i_count directly
on the inode.

Benchmarking shows this patch brings IOP/s on tons of flash up by about
2.5X.

Signed-off-by: Chris Mason <chris.mason@...cle.com>

diff --git a/fs/aio.c b/fs/aio.c
index cf0bef4..0be69fa 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1558,7 +1558,20 @@ static void aio_batch_add(struct address_space *mapping,
 	}
 
 	abe = mempool_alloc(abe_pool, GFP_KERNEL);
-	BUG_ON(!igrab(mapping->host));
+
+	/*
+	 * we should be using igrab here, but
+	 * we don't want to hammer on the global
+	 * inode spinlock just to take an extra
+	 * reference on a file that we must already
+	 * have a reference to.
+	 *
+	 * When we're called, we always have a reference
+	 * on the file, so we must always have a reference
+	 * on the inode, so igrab must always just
+	 * bump the count and move on.
+	 */
+	atomic_inc(&mapping->host->i_count);
 	abe->mapping = mapping;
 	hlist_add_head(&abe->list, &batch_hash[bucket]);
 	return;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/