linux-kernel - [PATCH 5.3 097/148] fuse: fix request limit

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Date:   Thu, 10 Oct 2019 10:35:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.3 097/148] fuse: fix request limit

From: Miklos Szeredi <mszeredi@...hat.com>

[ Upstream commit f22f812d5ce75a18b56073a7a63862e6ea764070 ]

The size of struct fuse_req was reduced from 392B to 144B on a non-debug
config, thus the sanitize_global_limit() helper was setting a larger
default limit.  This doesn't really reflect reduction in the memory used by
requests, since the fields removed from fuse_req were added to fuse_args
derived structs; e.g. sizeof(struct fuse_writepages_args) is 248B, thus
resulting in slightly more memory being used for writepage requests
overalll (due to using 256B slabs).

Make the calculatation ignore the size of fuse_req and use the old 392B
value.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/fuse/inode.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 987877860c019..f3104db3de83a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -823,9 +823,12 @@ static const struct super_operations fuse_super_operations = {
 
 static void sanitize_global_limit(unsigned *limit)
 {
+	/*
+	 * The default maximum number of async requests is calculated to consume
+	 * 1/2^13 of the total memory, assuming 392 bytes per request.
+	 */
 	if (*limit == 0)
-		*limit = ((totalram_pages() << PAGE_SHIFT) >> 13) /
-			 sizeof(struct fuse_req);
+		*limit = ((totalram_pages() << PAGE_SHIFT) >> 13) / 392;
 
 	if (*limit >= 1 << 16)
 		*limit = (1 << 16) - 1;
-- 
2.20.1