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Date: Wed, 11 May 2022 16:07:36 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Ritesh Harjani <ritesh.list@...il.com>
Cc: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
Ritesh Harjani <riteshh@...ux.ibm.com>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix journal_ioprio mount option handling
Hi Ritesh,
Thanks for taking the time to review this.
On Wed, May 11, 2022 at 01:18:53PM +0530, Ritesh Harjani wrote:
> On 22/04/18 02:05PM, Ojaswin Mujoo wrote:
> > In __ext4_super() we always overwrote the user specified journal_ioprio
> > value with a default value, expecting parse_apply_sb_mount_options() to
> > later correctly set ctx->journal_ioprio to the user specified value.
> > However, if parse_apply_sb_mount_options() returned early because of
> > empty sbi->es_s->s_mount_opts, the correct journal_ioprio value was
> > never set.
>
> >
> > This patch fixes __ext4_super() to only use the default value if the
> ^^^ __ext4_fill_super
Oops, will fix this in v2.
> > user has not specified any value for journal_ioprio.
>
> Also the problem is that ext4_parse_param() is called before
> __ext4_fill_super(). Hence when we overwrite ctx->journal_ioprio to default
> value in __ext4_fill_super(), that will end up ignoring the user passed
> journal_ioprio value via mount opts (which was passed earlier in
> ext4_parse_param()).
Right, I think my commit mesage is a bit incorrect in this regards. I
will fix this in v2.
>
>
> >
> > Similarly, the remount behavior was to either use journal_ioprio
> > value specified during initial mount, or use the default value
> > irrespective of the journal_ioprio value specified during remount.
> > This patch modifies this to first check if a new value for ioprio
> > has been passed during remount and apply it. Incase, no new value is
> > passed, use the value specified during initial mount.
>
> Yup, here also ext4_parse_param() is called before __ext4_remount().
> Hence we should check if the user has passed it's value in mount opts, if not,
> only then we should use the task original ioprio.
Yes correct.
>
>
> I tested this patch and with the patch applied, the task ioprio can be correctly
> set using "journal_ioprio" mount option.
>
> "Mount test"
> =============
> qemu-> sudo perf record -e probe:* -aR mount -o journal_ioprio=1 /dev/loop2 /mnt
> qemu-> ps -eaf |grep -E "jbd2|loop2"
> root 3506 2 0 07:41 ? 00:00:00 [jbd2/loop2-8]
> qemu-> sudo perf script
> mount 3504 [000] 2503.106871: probe:ext4_parse_param_L222: (ffffffff8147817f) journal_ioprio=16385 spec=32
> mount 3504 [000] 2503.106908: probe:__ext4_fill_super_L26: (ffffffff8147a650) journal_ioprio=16385 spec=32
> qemu-> ionice -p 3506
> best-effort: prio 1
>
> "remount test"
> =================
> qemu-> sudo perf record -e probe:* -aR mount -o remount,journal_ioprio=0 /dev/loop2 /mnt
> qemu-> sudo perf script
> mount 3519 [000] 2544.958850: probe:ext4_parse_param_L222: (ffffffff8147817f) journal_ioprio=16384 spec=32
> mount 3519 [000] 2544.958860: probe:__ext4_remount_L49: (ffffffff81479da2) journal_ioprio=16384 spec=32
> qemu-> ionice -p 3506
> best-effort: prio 0
>
> "remount with no mount options"
> =================================
> qemu-> sudo perf record -e probe:* -aR mount -o remount /dev/loop2 /mnt
> qemu-> ionice -p 3506
> best-effort: prio 0
> qemu-> sudo perf script
> mount 3530 [000] 2575.964048: probe:__ext4_remount_L49: (ffffffff81479da2) journal_ioprio=16384 spec=0
>
>
> >
> > Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
>
> We should add fixes tag too. Can you please confirm if that would be this patch?
> "ext4: Completely separate options parsing and sb setup".
Yes, it does seem like this issue was intorduced in this particular
commit. I'll add the Fixes tag.
>
> With that feel free to add below -
>
> Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> Tested-by: Ritesh Harjani <riteshh@...ux.ibm.com>
Thanks again for the review. I'll wait for a bit to see if we have any
more reviews and then send a v2 with the suggested changes.
Regards,
Ojaswin
>
>
> -ritesh
>
> > ---
> > fs/ext4/super.c | 15 ++++++++++-----
> > 1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index c5a9ffbf7f4f..bfd767c51203 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -4427,7 +4427,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
> > int silent = fc->sb_flags & SB_SILENT;
> >
> > /* Set defaults for the variables that will be set during parsing */
> > - ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> > + if (!(ctx->spec & EXT4_SPEC_JOURNAL_IOPRIO))
> > + ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> >
> > sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
> > sbi->s_sectors_written_start =
> > @@ -6289,7 +6290,6 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
> > char *to_free[EXT4_MAXQUOTAS];
> > #endif
> >
> > - ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> >
> > /* Store the original options */
> > old_sb_flags = sb->s_flags;
> > @@ -6315,9 +6315,14 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
> > } else
> > old_opts.s_qf_names[i] = NULL;
> > #endif
> > - if (sbi->s_journal && sbi->s_journal->j_task->io_context)
> > - ctx->journal_ioprio =
> > - sbi->s_journal->j_task->io_context->ioprio;
> > + if (!(ctx->spec & EXT4_SPEC_JOURNAL_IOPRIO)) {
> > + if (sbi->s_journal && sbi->s_journal->j_task->io_context)
> > + ctx->journal_ioprio =
> > + sbi->s_journal->j_task->io_context->ioprio;
> > + else
> > + ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> > +
> > + }
> >
> > ext4_apply_options(fc, sb);
> >
> > --
> > 2.27.0
> >
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