Re: [PATCH] btrfs: replace kcalloc() calls to kzalloc_objs()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/2/24 15:07, Qu Wenruo 写道:
> 
> 
> 在 2026/2/24 10:14, Miquel Sabaté Solà 写道:
>> Commit 2932ba8d9c99 ("slab: Introduce kmalloc_obj() and family")
>> introduced, among many others, the kzalloc_objs() helper, which has some
>> benefits over kcalloc().
>>
>> Cc: Kees Cook <kees@kernel.org>
>> Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
>> ---
>>   fs/btrfs/block-group.c       | 2 +-
>>   fs/btrfs/raid56.c            | 8 ++++----
>>   fs/btrfs/tests/zoned-tests.c | 2 +-
>>   fs/btrfs/volumes.c           | 6 ++----
>>   fs/btrfs/zoned.c             | 5 ++---
>>   5 files changed, 10 insertions(+), 13 deletions(-)
>>
>> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
>> index 37bea850b3f0..8d85b4707690 100644
>> --- a/fs/btrfs/block-group.c
>> +++ b/fs/btrfs/block-group.c
>> @@ -2239,7 +2239,7 @@ int btrfs_rmap_block(struct btrfs_fs_info 
>> *fs_info, u64 chunk_start,
>>       if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
>>           io_stripe_size = 
>> btrfs_stripe_nr_to_offset(nr_data_stripes(map));
>> -    buf = kcalloc(map->num_stripes, sizeof(u64), GFP_NOFS);
>> +    buf = kzalloc_objs(*buf, map->num_stripes, GFP_NOFS);
> 
> Not sure if we should use *buf for the type.
> 
> I still remember we had some bugs related to incorrect type usage.
> 
> Another thing is, we may not want to use the kzalloc version.
> We don't want to waste CPU time just to zero out the content meanwhile 
> we're ensured to re-assign the contents.
> 
> Thus kmalloc_objs() maybe better.

Sorry I only mean for some particular call sites, like this one.

Not all call sites can be converted to kmalloc version, and will need 
proper inspection one by one.

Thanks,
Qu

> 
> Thanks,
> Qu
> 
> 
>>       if (!buf) {
>>           ret = -ENOMEM;
>>           goto out;
>> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
>> index 02105d68accb..1ebfed8f0a0a 100644
>> --- a/fs/btrfs/raid56.c
>> +++ b/fs/btrfs/raid56.c
>> @@ -2110,8 +2110,8 @@ static int recover_sectors(struct btrfs_raid_bio 
>> *rbio)
>>        * @unmap_array stores copy of pointers that does not get reordered
>>        * during reconstruction so that kunmap_local works.
>>        */
>> -    pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>> -    unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>> +    pointers = kzalloc_objs(*pointers, rbio->real_stripes, GFP_NOFS);
>> +    unmap_array = kzalloc_objs(*unmap_array, rbio->real_stripes, 
>> GFP_NOFS);
>>       if (!pointers || !unmap_array) {
>>           ret = -ENOMEM;
>>           goto out;
>> @@ -2844,8 +2844,8 @@ static int recover_scrub_rbio(struct 
>> btrfs_raid_bio *rbio)
>>        * @unmap_array stores copy of pointers that does not get reordered
>>        * during reconstruction so that kunmap_local works.
>>        */
>> -    pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>> -    unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>> +    pointers = kzalloc_objs(*pointers, rbio->real_stripes, GFP_NOFS);
>> +    unmap_array = kzalloc_objs(*unmap_array, rbio->real_stripes, 
>> GFP_NOFS);
>>       if (!pointers || !unmap_array) {
>>           ret = -ENOMEM;
>>           goto out;
>> diff --git a/fs/btrfs/tests/zoned-tests.c b/fs/btrfs/tests/zoned-tests.c
>> index da21c7aea31a..2bc3b14baa41 100644
>> --- a/fs/btrfs/tests/zoned-tests.c
>> +++ b/fs/btrfs/tests/zoned-tests.c
>> @@ -58,7 +58,7 @@ static int test_load_zone_info(struct btrfs_fs_info 
>> *fs_info,
>>           return -ENOMEM;
>>       }
>> -    zone_info = kcalloc(test->num_stripes, sizeof(*zone_info), 
>> GFP_KERNEL);
>> +    zone_info = kzalloc_objs(*zone_info, test->num_stripes, GFP_KERNEL);
>>       if (!zone_info) {
>>           test_err("cannot allocate zone info");
>>           return -ENOMEM;
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index e15e138c515b..c0cf8f7c5a8e 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -5499,8 +5499,7 @@ static int calc_one_profile_avail(struct 
>> btrfs_fs_info *fs_info,
>>           goto out;
>>       }
>> -    devices_info = kcalloc(fs_devices->rw_devices, 
>> sizeof(*devices_info),
>> -                   GFP_NOFS);
>> +    devices_info = kzalloc_objs(*devices_info, fs_devices- 
>> >rw_devices, GFP_NOFS);
>>       if (!devices_info) {
>>           ret = -ENOMEM;
>>           goto out;
>> @@ -6067,8 +6066,7 @@ struct btrfs_block_group 
>> *btrfs_create_chunk(struct btrfs_trans_handle *trans,
>>       ctl.space_info = space_info;
>>       init_alloc_chunk_ctl(fs_devices, &ctl);
>> -    devices_info = kcalloc(fs_devices->rw_devices, 
>> sizeof(*devices_info),
>> -                   GFP_NOFS);
>> +    devices_info = kzalloc_objs(*devices_info, fs_devices- 
>> >rw_devices, GFP_NOFS);
>>       if (!devices_info)
>>           return ERR_PTR(-ENOMEM);
>> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
>> index ab330ec957bc..851b0de7bed7 100644
>> --- a/fs/btrfs/zoned.c
>> +++ b/fs/btrfs/zoned.c
>> @@ -1697,8 +1697,7 @@ static int btrfs_load_block_group_raid10(struct 
>> btrfs_block_group *bg,
>>           return -EINVAL;
>>       }
>> -    raid0_allocs = kcalloc(map->num_stripes / map->sub_stripes, 
>> sizeof(*raid0_allocs),
>> -                   GFP_NOFS);
>> +    raid0_allocs = kzalloc_objs(*raid0_allocs, map->num_stripes / 
>> map->sub_stripes, GFP_NOFS);
>>       if (!raid0_allocs)
>>           return -ENOMEM;
>> @@ -1916,7 +1915,7 @@ int btrfs_load_block_group_zone_info(struct 
>> btrfs_block_group *cache, bool new)
>>       cache->physical_map = map;
>> -    zone_info = kcalloc(map->num_stripes, sizeof(*zone_info), GFP_NOFS);
>> +    zone_info = kzalloc_objs(*zone_info, map->num_stripes, GFP_NOFS);
>>       if (!zone_info) {
>>           ret = -ENOMEM;
>>           goto out;
> 
>