Re: [PATCH 1/4] fs/erofs: align the malloc'ed data

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2026/3/23 23:08, Michael Walle wrote:
> Hi Gao,
> 
> On Mon Mar 23, 2026 at 3:41 PM CET, Gao Xiang wrote:
>> Hi Michael,
>>
>> On 2026/3/23 21:42, Michael Walle wrote:
>>> The data buffers are used to transfer from or to hardware peripherals.
>>> Often, there are restrictions on addresses, i.e. they have to be aligned
>>> at a certain size. Thus, allocate the data on the heap instead of the
>>> stack (at a random address alignment). Use malloc_cache_aligned() to get
>>> an aligned buffer.
>>
>> Many thanks for the patch, I wonder if it's possible to
>> submit the patches to erofs-utils first (even make
>> malloc_cache_aligned() as another malloc() for example)?
>>
>> Since I'd like to make u-boot codebase following
>> erofs-utils, but I don't think Jianan have the
>> bandwidth now, but if you have some use cases,
>> you could help syncing up a bit.
> 
> Sorry, I don't have the bandwidth neither. But now I see where all
> this is coming from. In userspace, you have much less (or none at
> all) restrictions. So not sure, if that even makes sense to share. As
> you've already pointed out the malloc_cache_aligned() would have to
> be changed (back!) to malloc() again.

But it can align the codebase between erofs-utils and u-boot,
in that way, all potential bug fixes can be addressed
together.

> 
>> Or at least, let's keep these four patches in sync
>> between erofs-utils and u-boot.
> 
> Not sure what a DMA alignment has to do with userspace, or do you
> mean moving all the block data from stack to heap?

I think if it's not complex, we could do that, but if some
case is very hard, we can leave them alone.

> 
> This is more or less the result from an internal evaluation. You (or
> anybody else) might take it - or leave it.
> 
> Do you share code between linux and erofs-utils, too? How does that
> work?

Only the majority of metadata parsing logic is shared by
the linux kernel and erofs-utils, much like XFS shares
libxfs between the kernel and xfsprogs.

Thanks,
Gao Xiang
  
> 
> Thanks,
> -michael
> 
>>
>> Many thanks!
>> Gao Xiang
>>
>>>
>>> Signed-off-by: Michael Walle <mwalle@kernel.org>
>>> ---
>>>    fs/erofs/data.c     | 11 ++++-------
>>>    fs/erofs/internal.h |  1 +
>>>    2 files changed, 5 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
>>> index b58ec6fcc66..61dbae51a9a 100644
>>> --- a/fs/erofs/data.c
>>> +++ b/fs/erofs/data.c
>>> @@ -319,15 +319,13 @@ static int z_erofs_read_data(struct erofs_inode *inode, char *buffer,
>>>    		}
>>>    
>>>    		if (map.m_plen > bufsize) {
>>> -			char *tmp;
>>> -
>>>    			bufsize = map.m_plen;
>>> -			tmp = realloc(raw, bufsize);
>>> -			if (!tmp) {
>>> +			free(raw);
>>> +			raw = malloc_cache_aligned(bufsize);
>>> +			if (!raw) {
>>>    				ret = -ENOMEM;
>>>    				break;
>>>    			}
>>> -			raw = tmp;
>>>    		}
>>>    
>>>    		ret = z_erofs_read_one_data(inode, &map, raw,
>>> @@ -336,8 +334,7 @@ static int z_erofs_read_data(struct erofs_inode *inode, char *buffer,
>>>    		if (ret < 0)
>>>    			break;
>>>    	}
>>> -	if (raw)
>>> -		free(raw);
>>> +	free(raw);
>>>    	return ret < 0 ? ret : 0;
>>>    }
>>>    
>>> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
>>> index 1875f37fcd2..13c862325a6 100644
>>> --- a/fs/erofs/internal.h
>>> +++ b/fs/erofs/internal.h
>>> @@ -11,6 +11,7 @@
>>>    #include <linux/printk.h>
>>>    #include <linux/log2.h>
>>>    #include <inttypes.h>
>>> +#include <memalign.h>
>>>    #include "erofs_fs.h"
>>>    
>>>    #define erofs_err(fmt, ...)	\
>