Re: [PATCH 1/1] f2fs: allocate trace path buffer from names_cache

[Chao Yu]

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@xxxxxxxx>
> > > ---
> > >    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@xxxxxxxxxx>

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)