linux-kernel - [PATCH] bcachefs: Avoid a potential memory over-allocation in bch2_printbuf_make

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Message-Id: <2e6a82a83d0ddd9ce7f36ea889dd7ffc30f5fbc9.1694853900.git.christophe.jaillet@wanadoo.fr>
Date:   Sat, 16 Sep 2023 10:45:23 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Kent Overstreet <kent.overstreet@...ux.dev>,
        Brian Foster <bfoster@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-bcachefs@...r.kernel.org
Subject: [PATCH] bcachefs: Avoid a potential memory over-allocation in bch2_printbuf_make_room()

kmalloc() and co. don't always allocate a power of 2 number of bytes.
There are some special handling for 64<n<=96 and 128<n<=192 cases.

So trust kmalloc() algorithm instead of forcing a power of 2 allocation.
This can saves a few bytes of memory and still make use of all the
memory allocated.

On the other side, it may require an additional realloc() in some cases.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 fs/bcachefs/printbuf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/bcachefs/printbuf.c b/fs/bcachefs/printbuf.c
index 77bee9060bfe..34527407e950 100644
--- a/fs/bcachefs/printbuf.c
+++ b/fs/bcachefs/printbuf.c
@@ -28,7 +28,7 @@ int bch2_printbuf_make_room(struct printbuf *out, unsigned extra)
 	if (out->pos + extra < out->size)
 		return 0;
 
-	new_size = roundup_pow_of_two(out->size + extra);
+	new_size = kmalloc_size_roundup(out->size + extra);
 
 	/*
 	 * Note: output buffer must be freeable with kfree(), it's not required
-- 
2.34.1