Andreas Dilger <adilger@xxxxxxxxx> 于2023年7月21日周五 06:50写道： > > On May 9, 2023, at 6:14 PM, JunChao Sun <sunjunchao2870@xxxxxxxxx> wrote: > > > > 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. > > Sorry for the long delay in reviewing this patch. > > The performance gains are nice, and reducing overhead is always good. > > > > One question about this patch is whether it is safe to overwrite the > > xattr in place if the system crashes during the overwrite? That was > > one of the reasons why the xattr update was implemented by writing to > > a new xattr inode, and then atomically swapping xattr inode numbers. > > > > However, if the xattr overwrite is done via journaled data writes then > > it would be safe to "overwrite" the xattr data "in place", because > > data will first be committed to the journal and then checkpointed into > > the inode itself, so it should never be inconsistent/corrupted. Thanks for your review. I'm sorry for taking so long to reply.. I checked the relevant code, and ensured that xattr overwriting is done via journal, so it should be safe. > > > > Did you also test cases where the xattr size is growing or shrinking > > during the overwrite in place? That should allocate or free blocks > > in the xattr inode so that they are not wasted. > > Here is a bug in this patch, when xattr size is shrinking, blocks that were previously allocated but need to be released now will not be released. Here may need a ext4_truncate to release redundant blocks. I will check ext4_truncate function and test relative cases, and then send patch v3. > Cheers, Andreas > > > 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 takes > > 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@xxxxxxxxx> > > --- > > > > 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@xxxxxxxxx/ > > > > 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_inode) { > > + /* Replace xattr value in ea_inode in place */ > > + int size_diff = i->value_len - le32_to_cpu(here->e_value_size); > > + > > + ret = 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 = NULL; > > + goto out; > > + } > > + if (ext4_xattr_inode_get_ref(old_ea_inode) == 1) { > > + if (size_diff > 0) > > + ret = ext4_xattr_inode_alloc_quota(inode, size_diff); > > + else if (size_diff < 0) > > + ext4_xattr_inode_free_quota(inode, NULL, -size_diff); > > + if (ret) > > + goto out; > > + > > + ret = ext4_xattr_inode_write(handle, old_ea_inode, 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 = ext4_xattr_inode_alloc_quota(inode, -size_diff); > > + goto out; > > + } > > + here->e_value_size = cpu_to_le32(i->value_len); > > + new_ea_inode = old_ea_inode; > > + old_ea_inode = 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 data. > > -- > > 1.8.3.1 > > > > > Cheers, Andreas > > > > >
