From: Weixie Cui Date: Wed, 25 Feb 2026 05:02:31 +0000 (+0800) Subject: ext4: simplify mballoc preallocation size rounding for small files X-Git-Url: http://git.ipfire.org/index.cgi?a=commitdiff_plain;h=af1502f98e2cdd43504596cd438f3aa6d0be8712;p=thirdparty%2Fkernel%2Flinux.git ext4: simplify mballoc preallocation size rounding for small files The if-else ladder in ext4_mb_normalize_request() manually rounds up the preallocation size to the next power of two for files up to 1MB, enumerating each step from 16KB to 1MB individually. Replace this with a single roundup_pow_of_two() call clamped to a 16KB minimum, which is functionally equivalent but much more concise. Also replace raw byte constants with SZ_1M and SZ_16K from for clarity, and remove the stale "XXX: should this table be tunable?" comment that has been there since the original mballoc code. No functional change. Reviewed-by: Andreas Dilger Signed-off-by: Weixie Cui Link: https://patch.msgid.link/tencent_E9C5F1B2E9939B3037501FD04A7E9CF0C407@qq.com Signed-off-by: Theodore Ts'o --- diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index bb58eafb87bcd..3d73f64fc49a0 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -4561,22 +4561,16 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac, (req <= (size) || max <= (chunk_size)) /* first, try to predict filesize */ - /* XXX: should this table be tunable? */ start_off = 0; - if (size <= 16 * 1024) { - size = 16 * 1024; - } else if (size <= 32 * 1024) { - size = 32 * 1024; - } else if (size <= 64 * 1024) { - size = 64 * 1024; - } else if (size <= 128 * 1024) { - size = 128 * 1024; - } else if (size <= 256 * 1024) { - size = 256 * 1024; - } else if (size <= 512 * 1024) { - size = 512 * 1024; - } else if (size <= 1024 * 1024) { - size = 1024 * 1024; + if (size <= SZ_1M) { + /* + * For files up to 1MB, round up the preallocation size to + * the next power of two, with a minimum of 16KB. + */ + if (size <= (unsigned long)SZ_16K) + size = SZ_16K; + else + size = roundup_pow_of_two(size); } else if (NRL_CHECK_SIZE(size, 4 * 1024 * 1024, max, 2 * 1024)) { start_off = ((loff_t)ac->ac_o_ex.fe_logical >> (21 - bsbits)) << 21;