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From: Amir Goldstein <amir73il@gmail.com>
To: Chengguang Xu <cgxu519@mykernel.net>
Cc: miklos <miklos@szeredi.hu>, jack <jack@suse.cz>,
	linux-unionfs <linux-unionfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH v3 09/10] ovl: introduce helper of syncfs writeback inode waiting
Date: Mon, 9 Nov 2020 12:07:18 +0200
Message-ID: <CAOQ4uxgfi26HDp6YWx3Tgc1tY_EMrfcW_hz5FMG8vXeHLdycBw@mail.gmail.com> (raw)
In-Reply-To: <175ac242078.1287a39451704.7442694321257329129@mykernel.net>

On Mon, Nov 9, 2020 at 10:34 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
>  ---- 在 星期一, 2020-11-09 15:07:18 Amir Goldstein <amir73il@gmail.com> 撰写 ----
>  > On Mon, Nov 9, 2020 at 5:34 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>  > >
>  > >  ---- 在 星期日, 2020-11-08 22:03:06 Chengguang Xu <cgxu519@mykernel.net> 撰写 ----
>  > >  > Introduce a helper ovl_wait_wb_inodes() to wait until all
>  > >  > target upper inodes finish writeback.
>  > >  >
>  > >  > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
>  > >  > ---
>  > >  >  fs/overlayfs/super.c | 30 ++++++++++++++++++++++++++++++
>  > >  >  1 file changed, 30 insertions(+)
>  > >  >
>  > >  > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
>  > >  > index e5607a908d82..9a535fc11221 100644
>  > >  > --- a/fs/overlayfs/super.c
>  > >  > +++ b/fs/overlayfs/super.c
>  > >  > @@ -255,6 +255,36 @@ static void ovl_put_super(struct super_block *sb)
>  > >  >      ovl_free_fs(ofs);
>  > >  >  }
>  > >  >
>  > >  > +void ovl_wait_wb_inodes(struct ovl_fs *ofs)
>  > >  > +{
>  > >  > +    LIST_HEAD(tmp_list);
>  > >  > +    struct ovl_inode *oi;
>  > >  > +    struct inode *upper;
>  > >  > +
>  > >  > +    spin_lock(&ofs->syncfs_wait_list_lock);
>  > >  > +    list_splice_init(&ofs->syncfs_wait_list, &tmp_list);
>  > >  > +
>  > >  > +    while (!list_empty(&tmp_list)) {
>  > >  > +        oi = list_first_entry(&tmp_list, struct ovl_inode, wait_list);
>  > >  > +        list_del_init(&oi->wait_list);
>  > >  > +        ihold(&oi->vfs_inode);
>  > >
>  > > Maybe I overlooked race condition with inode eviction, so still need to introduce
>  > > OVL_EVICT_PENDING flag just like we did in old syncfs efficiency patch series.
>  > >
>  >
>  > I am not sure why you added the ovl wait list.
>  >
>  > I think you misunderstood Jan's suggestion.
>  > I think what Jan meant is that ovl_sync_fs() should call
>  > wait_sb_inodes(upper_sb)
>  > to wait for writeback of ALL upper inodes after sync_filesystem()
>  > started writeback
>  > only on this ovl instance upper inodes.
>  >
>
>
> Maybe you are right, the wait list is just for accuracy that can completely
> avoid interferes between ovl instances, otherwise we may need to face
> waiting interferes  in high density environment.
>
>
>  > I am not sure if this is acceptable or not - it is certainly an improvement over
>  > current situation, but I have a feeling that on a large scale (many
>  > containers) it
>  > won't be enough.
>  >
>
> The same as your thought.
>
>
>  > The idea was to keep it simple without over optimizing, since anyway
>  > you are going for the "correct" solution long term (ovl inode aops),
>  > so I wouldn't
>  > add the wait list.
>  >
>
> Maybe, I think it depends on how to implement ovl page-cache, so at current
> stage I have no idea for the wait list.
>
>
>  > As long as the upper inode is still dirty, we can keep the ovl inode in cache,
>  > so the worst outcome is that drop_caches needs to get called twice before the
>  > ovl inode can be evicted, no?
>  >
>
> IIUC, since currently ovl does not have it's own page-cache, so there is no affect to page-cache reclaim,
> also  there is no ovl shrinker to reclaim slab because we drop ovl inode directly after final iput.
> So should we add a shrinker in this series?
>

Would that add a lot of complexity?
Thinking out loud: maybe we follow Jan's suggestion and fix remaining
performance with followup series?

Thanks,
Amir.

  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-08 14:02 [RFC PATCH v3 00/10] implement containerized syncfs for overlayfs Chengguang Xu
2020-11-08 14:02 ` [RFC PATCH v3 01/10] ovl: setup overlayfs' private bdi Chengguang Xu
2020-11-08 14:02 ` [RFC PATCH v3 02/10] ovl: introduce waiting list for syncfs Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 03/10] ovl: implement ->writepages operation Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 04/10] ovl: implement overlayfs' ->evict_inode operation Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 05/10] ovl: mark overlayfs' inode dirty on modification Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 06/10] ovl: mark overlayfs' inode dirty on shared mmap Chengguang Xu
2020-11-11 13:05   ` 回复:[RFC " Chengguang Xu
2020-11-11 15:20     ` [RFC " Amir Goldstein
2020-11-11 16:09       ` Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 07/10] ovl: implement overlayfs' ->write_inode operation Chengguang Xu
2020-11-10 13:45   ` Jan Kara
2020-11-10 15:12     ` Chengguang Xu
2020-11-11 10:54       ` Jan Kara
2020-11-10 16:18     ` Amir Goldstein
2020-11-08 14:03 ` [RFC PATCH v3 08/10] ovl: cache dirty overlayfs' inode Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 09/10] ovl: introduce helper of syncfs writeback inode waiting Chengguang Xu
2020-11-09  3:33   ` 回复:[RFC " Chengguang Xu
2020-11-09  7:07     ` [RFC " Amir Goldstein
2020-11-09  8:34       ` Chengguang Xu
2020-11-09 10:07         ` Amir Goldstein [this message]
2020-11-09 12:06           ` Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 10/10] ovl: implement containerized syncfs for overlayfs Chengguang Xu

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