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Message-ID: <20251208083246.320965-2-yukuai@fnnas.com>
Date: Mon, 8 Dec 2025 16:32:45 +0800
From: Yu Kuai <yukuai@...as.com>
To: tytso@....edu,
adilger.kernel@...ger.ca,
linux-ext4@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
yukuai@...as.com
Subject: [PATCH 1/2] ext4: refactor size prediction into helper functions
The ext4_mb_normalize_request() function contains a large if-else
ladder for predicting file size and uses a macro NRL_CHECK_SIZE.
Factor these out into proper helper functions to improve code
readability and maintainability.
This patch introduces:
- ext4_mb_check_size(): static inline function replacing NRL_CHECK_SIZE macro
- ext4_mb_predict_file_size(): extracts size prediction logic
No functional change.
Signed-off-by: Yu Kuai <yukuai@...as.com>
---
fs/ext4/mballoc.c | 101 +++++++++++++++++++++++++++-------------------
1 file changed, 60 insertions(+), 41 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 9087183602e4..eb46a4f5fb4f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4489,6 +4489,63 @@ ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
*end = new_end;
}
+/*
+ * Check if request size allows for chunk-based allocation
+ */
+static inline bool ext4_mb_check_size(loff_t req, loff_t size,
+ int max, int chunk_size)
+{
+ return (req <= size) || (max <= chunk_size);
+}
+
+/*
+ * Predict file size for preallocation. Returns the predicted size
+ * in bytes and sets start_off if alignment is needed for large files.
+ */
+static loff_t ext4_mb_predict_file_size(struct ext4_sb_info *sbi,
+ struct ext4_allocation_context *ac,
+ loff_t size, loff_t *start_off)
+{
+ int bsbits = ac->ac_sb->s_blocksize_bits;
+ int max = 2 << bsbits;
+
+ *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;
+ } else if (ext4_mb_check_size(size, 4 * 1024 * 1024, max, 2 * 1024)) {
+ *start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
+ (21 - bsbits)) << 21;
+ size = 2 * 1024 * 1024;
+ } else if (ext4_mb_check_size(size, 8 * 1024 * 1024, max, 4 * 1024)) {
+ *start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
+ (22 - bsbits)) << 22;
+ size = 4 * 1024 * 1024;
+ } else if (ext4_mb_check_size(EXT4_C2B(sbi, ac->ac_o_ex.fe_len),
+ (8<<20)>>bsbits, max, 8 * 1024)) {
+ *start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
+ (23 - bsbits)) << 23;
+ size = 8 * 1024 * 1024;
+ } else {
+ *start_off = (loff_t)ac->ac_o_ex.fe_logical << bsbits;
+ size = (loff_t)EXT4_C2B(sbi, ac->ac_o_ex.fe_len) << bsbits;
+ }
+
+ return size;
+}
+
/*
* Normalization means making request better in terms of
* size and alignment
@@ -4500,7 +4557,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
struct ext4_super_block *es = sbi->s_es;
int bsbits, max;
- loff_t size, start_off, end;
+ loff_t size, start_off = 0, end;
loff_t orig_size __maybe_unused;
ext4_lblk_t start;
@@ -4533,47 +4590,9 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
size = i_size_read(ac->ac_inode);
orig_size = size;
- /* max size of free chunks */
- max = 2 << bsbits;
+ /* Predict file size for preallocation */
+ size = ext4_mb_predict_file_size(sbi, ac, size, &start_off);
-#define NRL_CHECK_SIZE(req, size, max, chunk_size) \
- (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;
- } 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;
- size = 2 * 1024 * 1024;
- } else if (NRL_CHECK_SIZE(size, 8 * 1024 * 1024, max, 4 * 1024)) {
- start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
- (22 - bsbits)) << 22;
- size = 4 * 1024 * 1024;
- } else if (NRL_CHECK_SIZE(EXT4_C2B(sbi, ac->ac_o_ex.fe_len),
- (8<<20)>>bsbits, max, 8 * 1024)) {
- start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
- (23 - bsbits)) << 23;
- size = 8 * 1024 * 1024;
- } else {
- start_off = (loff_t) ac->ac_o_ex.fe_logical << bsbits;
- size = (loff_t) EXT4_C2B(sbi,
- ac->ac_o_ex.fe_len) << bsbits;
- }
size = size >> bsbits;
start = start_off >> bsbits;
--
2.51.0
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