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From: Yafang Shao <laoar.shao@gmail.com>
To: kees@kernel.org,
joel.granados@kernel.org
Cc: linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org,
Yafang Shao <laoar.shao@gmail.com>,
Josef Bacik <josef@toxicpanda.com>
Subject: [PATCH] proc: Avoid costly high-order page allocations when reading
proc files
Date: Tue, 1 Apr 2025 15:30:46 +0800
Message-Id: <20250401073046.51121-1-laoar.shao@gmail.com>
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While investigating a kcompactd 100% CPU utilization issue in production, I
observed frequent costly high-order (order-6) page allocations triggered by
proc file reads from monitoring tools. This can be reproduced with a simple
test case:
fd =3D open(PROC_FILE, O_RDONLY);
size =3D read(fd, buff, 256KB);
close(fd);
Although we should modify the monitoring tools to use smaller buffer sizes,
we should also enhance the kernel to prevent these expensive high-order
allocations.
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Josef Bacik <josef@toxicpanda.com>
---
fs/proc/proc_sysctl.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index cc9d74a06ff0..c53ba733bda5 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -581,7 +581,15 @@ static ssize_t proc_sys_call_handler(struct kiocb *ioc=
b, struct iov_iter *iter,
error =3D -ENOMEM;
if (count >=3D KMALLOC_MAX_SIZE)
goto out;
- kbuf =3D kvzalloc(count + 1, GFP_KERNEL);
+
+ /*
+ * Use vmalloc if the count is too large to avoid costly high-order page
+ * allocations.
+ */
+ if (count < (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
+ kbuf =3D kvzalloc(count + 1, GFP_KERNEL);
+ else
+ kbuf =3D vmalloc(count + 1);
if (!kbuf)
goto out;
=20
--=20
2.43.5