linux-kernel - Re: [PATCH 1/1] f2fs: allocate trace path buffer from names

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Message-ID: <91a05857-c916-cae5-d61d-bbec6f1ae052@kernel.org>
Date:   Wed, 19 Apr 2023 14:28:33 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Wu Bo <bo.wu@...o.com>, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, wubo.oduw@...il.com
Subject: Re: [PATCH 1/1] f2fs: allocate trace path buffer from names_cache

On 2023/4/19 0:07, Jaegeuk Kim wrote:
> On 04/18, Chao Yu wrote:
>> On 2023/4/14 18:43, Wu Bo wrote:
>>> It would be better to use the dedicated slab to store path.
>>>
>>> Signed-off-by: Wu Bo <bo.wu@...o.com>
>>> ---
>>>    fs/f2fs/file.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 15dabeac4690..27137873958f 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -4361,7 +4361,7 @@ static void f2fs_trace_rw_file_path(struct kiocb *iocb, size_t count, int rw)
>>>    	struct inode *inode = file_inode(iocb->ki_filp);
>>>    	char *buf, *path;
>>> -	buf = f2fs_kmalloc(F2FS_I_SB(inode), PATH_MAX, GFP_KERNEL);
>>> +	buf = __getname();
>>
>> How about:
>>
>> buf = f2fs_kmem_cache_alloc(names_cachep, GFP_KERNEL, NULL, F2FS_I_SB(inode));
> 
> This looks like a hack using names_cachep?

names_cachep was exported in fs.h.

 > Using f2fs_kmem_cache_alloc is able to inject malloc error.
 > But here is a trace event, is it ok to inject error in a trace path?

Yes, the fail path handling is very simple, so it's fine to leave it
as it is.

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,

> 
>>
>>>    	if (!buf)
>>>    		return;
>>>    	path = dentry_path_raw(file_dentry(iocb->ki_filp), buf, PATH_MAX);
>>> @@ -4374,7 +4374,7 @@ static void f2fs_trace_rw_file_path(struct kiocb *iocb, size_t count, int rw)
>>>    		trace_f2fs_dataread_start(inode, iocb->ki_pos, count,
>>>    				current->pid, path, current->comm);
>>>    free_buf:
>>> -	kfree(buf);
>>> +	__putname(buf);
>>
>> kmem_cache_free(names_cachep, buf);
>>
>> Thanks,
>>
>>>    }
>>>    static ssize_t f2fs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)