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From:   JunChao Sun <sunjunchao2870@gmail.com>
Date:   Tue, 23 May 2023 20:06:44 +0800
Message-ID: <CAHB1NahwmPEm8dT=27y8rQ0ZBBe6HC7jwM4F0XchJhKTZLhkqQ@mail.gmail.com>
Subject: Re: [PATCH v2] ext4: Replace value of xattrs in place
To:     tytso@mit.edu, adilger.kernel@dilger.ca
Cc:     jack@suse.cz, linux-ext4@vger.kernel.org
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Friendly ping...
Could anyone review this patch?

JunChao Sun <sunjunchao2870@gmail.com> =E4=BA=8E2023=E5=B9=B45=E6=9C=8810=
=E6=97=A5=E5=91=A8=E4=B8=89 08:14=E5=86=99=E9=81=93=EF=BC=9A
>
> When replacing the value of an xattr found in an ea_inode, currently
> ext4 will evict the ea_inode that stores the old value, recreate an
> ea_inode, and then write the new value into the new ea_inode.
> This can be optimized by writing the new value into the old
> ea_inode directly.
>
> The logic for replacing value of xattrs without this patch
> is as follows:
> ext4_xattr_set_entry()
>     ->ext4_xattr_inode_iget(&old_ea_inode)
>     ->ext4_xattr_inode_lookup_create(&new_ea_inode)
>     ->ext4_xattr_inode_dec_ref(old_ea_inode)
>     ->iput(old_ea_inode)
>         ->ext4_destroy_inode()
>         ->ext4_evict_inode()
>         ->ext4_free_inode()
>     ->iput(new_ea_inode)
>
> The logic with this patch is:
> ext4_xattr_set_entry()
>     ->ext4_xattr_inode_iget(&old_ea_inode)
>     ->ext4_xattr_inode_write(old_ea_inode, new_value)
>     ->iput(old_ea_inode)
>
> This patch reduces the time it takes to replace xattrs in the ext4.
> Without this patch, replacing the value of an xattr two million times tak=
es
> about 45 seconds on Intel(R) Xeon(R) CPU E5-2620 v3 platform.
> With this patch, the same operation takes only 6 seconds.
>
>   [root@client01 sjc]# ./mount.sh
>   /dev/sdb1 contains a ext4 file system
>       last mounted on /mnt/ext4 on Mon May  8 17:05:38 2023
>   [root@client01 sjc]# touch /mnt/ext4/file1
>   [root@client01 sjc]# gcc test.c
>   [root@client01 sjc]# time ./a.out
>
>   real    0m45.248s
>   user    0m0.513s
>   sys 0m39.231s
>
>   [root@client01 sjc]# ./mount.sh
>   /dev/sdb1 contains a ext4 file system
>       last mounted on /mnt/ext4 on Mon May  8 17:08:20 2023
>   [root@client01 sjc]# touch /mnt/ext4/file1
>   [root@client01 sjc]# time ./a.out
>
>   real    0m5.977s
>   user    0m0.316s
>   sys 0m5.659s
>
> The test.c and mount.sh are in [1].
> This patch passed the tests with xfstests using 'check -g quick'.
>
> [1] https://gist.github.com/sjc2870/c923d7fa627d10ab65d6c305afb02cdb
>
> Signed-off-by: JunChao Sun <sunjunchao2870@gmail.com>
> ---
>
> Changes in v2:
>   - Fix a problem when ref of an ea_inode not equal to 1
>   - Link to v1: https://lore.kernel.org/linux-ext4/20230509011042.11781-1=
-sunjunchao2870@gmail.com/
>
>  fs/ext4/xattr.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index d57408cbe903..8f03958bfcc6 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1713,6 +1713,42 @@ static int ext4_xattr_set_entry(struct ext4_xattr_=
info *i,
>                 }
>         }
>
> +       if (!s->not_found && i->value && here->e_value_inum && i->in_inod=
e) {
> +               /* Replace xattr value in ea_inode in place */
> +               int size_diff =3D i->value_len - le32_to_cpu(here->e_valu=
e_size);
> +
> +               ret =3D ext4_xattr_inode_iget(inode,
> +                                               le32_to_cpu(here->e_value=
_inum),
> +                                               le32_to_cpu(here->e_hash)=
,
> +                                               &old_ea_inode);
> +               if (ret) {
> +                       old_ea_inode =3D NULL;
> +                       goto out;
> +               }
> +               if (ext4_xattr_inode_get_ref(old_ea_inode) =3D=3D 1) {
> +                       if (size_diff > 0)
> +                               ret =3D ext4_xattr_inode_alloc_quota(inod=
e, size_diff);
> +                       else if (size_diff < 0)
> +                               ext4_xattr_inode_free_quota(inode, NULL, =
-size_diff);
> +                       if (ret)
> +                               goto out;
> +
> +                       ret =3D ext4_xattr_inode_write(handle, old_ea_ino=
de, i->value, i->value_len);
> +                       if (ret) {
> +                               if (size_diff > 0)
> +                                       ext4_xattr_inode_free_quota(inode=
, NULL, size_diff);
> +                               else if (size_diff < 0)
> +                                       ret =3D ext4_xattr_inode_alloc_qu=
ota(inode, -size_diff);
> +                               goto out;
> +                       }
> +                       here->e_value_size =3D cpu_to_le32(i->value_len);
> +                       new_ea_inode =3D old_ea_inode;
> +                       old_ea_inode =3D NULL;
> +                       goto update_hash;
> +               } else
> +                       iput(old_ea_inode);
> +       }
> +
>         /*
>          * Getting access to old and new ea inodes is subject to failures=
.
>          * Finish that work before doing any modifications to the xattr d=
ata.
> --
> 1.8.3.1
>