Re: [PATCH 1/1] quota: Fix slow quotaoff

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Oct 12, 2023 at 02:25:33PM +0200, Zbigniew Lukwinski wrote:
> From: Jan Kara <jack@suse.cz>
> 
> Eric has reported that commit dabc8b207566 ("quota: fix dqput() to
> follow the guarantees dquot_srcu should provide") heavily increases
> runtime of generic/270 xfstest for ext4 in nojournal mode. The reason
> for this is that ext4 in nojournal mode leaves dquots dirty until the last
> dqput() and thus the cleanup done in quota_release_workfn() has to write
> them all. Due to the way quota_release_workfn() is written this results
> in synchronize_srcu() call for each dirty dquot which makes the dquot
> cleanup when turning quotas off extremely slow.
> 
> To be able to avoid synchronize_srcu() for each dirty dquot we need to
> rework how we track dquots to be cleaned up. Instead of keeping the last
> dquot reference while it is on releasing_dquots list, we drop it right
> away and mark the dquot with new DQ_RELEASING_B bit instead. This way we
> can we can remove dquot from releasing_dquots list when new reference to
> it is acquired and thus there's no need to call synchronize_srcu() each
> time we drop dq_list_lock.
> 
> References: https://lore.kernel.org/all/ZRytn6CxFK2oECUt@debian-BULLSEYE-live-builder-AMD64
> Reported-by: Eric Whitney <enwlinux@gmail.com>
> Fixes: dabc8b207566 ("quota: fix dqput() to follow the guarantees dquot_srcu should provide")
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/quota/dquot.c         | 66 ++++++++++++++++++++++++----------------
>  include/linux/quota.h    |  4 ++-
>  include/linux/quotaops.h |  2 +-
>  3 files changed, 43 insertions(+), 29 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>