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ext4: reduce unnecessary memory allocation in alloc_flex_gd()

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When a large flex_bg file system is resized, the number of groups to be
added may be small, and a large amount of memory that will not be used will
be allocated. Therefore, resize_bg can be set to the size after the number
of new_group_data to be used is aligned upwards to the power of 2. This
does not affect the disk layout after online resize and saves some memory.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231023013057.2117948-5-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li 2023-10-23 09:30:57 +08:00 • committed by Theodore Ts'o
parent 5d1935ac02
commit 665d3e0af4
1 changed files with 12 additions and 2 deletions
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14
fs/ext4/resize.c
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@ -235,8 +235,10 @@ struct ext4_new_flex_group_data {
* *
* Returns NULL on failure otherwise address of the allocated structure. * Returns NULL on failure otherwise address of the allocated structure.
*/ */
static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size) static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size,
ext4_group_t o_group, ext4_group_t n_group)
{ {
ext4_group_t last_group;
struct ext4_new_flex_group_data *flex_gd; struct ext4_new_flex_group_data *flex_gd;
flex_gd = kmalloc(sizeof(*flex_gd), GFP_NOFS); flex_gd = kmalloc(sizeof(*flex_gd), GFP_NOFS);
@ -248,6 +250,14 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size)
else else
flex_gd->resize_bg = flexbg_size; flex_gd->resize_bg = flexbg_size;
/* Avoid allocating large 'groups' array if not needed */
last_group = o_group | (flex_gd->resize_bg - 1);
if (n_group <= last_group)
flex_gd->resize_bg = 1 << fls(n_group - o_group + 1);
else if (n_group - last_group < flex_gd->resize_bg)
flex_gd->resize_bg = 1 << max(fls(last_group - o_group + 1),
fls(n_group - last_group));
flex_gd->groups = kmalloc_array(flex_gd->resize_bg, flex_gd->groups = kmalloc_array(flex_gd->resize_bg,
sizeof(struct ext4_new_group_data), sizeof(struct ext4_new_group_data),
GFP_NOFS); GFP_NOFS);
@ -2131,7 +2141,7 @@ retry:
if (err) if (err)
goto out; goto out;
flex_gd = alloc_flex_gd(flexbg_size); flex_gd = alloc_flex_gd(flexbg_size, o_group, n_group);
if (flex_gd == NULL) { if (flex_gd == NULL) {
err = -ENOMEM; err = -ENOMEM;
goto out; goto out;