linux-kernel - Re: [PATCH] fuse_writepages_fill() optimization to avoid WARN_ON in tree

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Date:   Tue, 14 Jul 2020 14:40:47 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Vasily Averin <vvs@...tuozzo.com>, linux-fsdevel@...r.kernel.org,
        Maxim Patlasov <maximvp@...il.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fuse_writepages_fill() optimization to avoid WARN_ON in tree_insert

On Mon, Jul 13, 2020 at 6:16 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Mon, Jul 13, 2020 at 10:02 AM Vasily Averin <vvs@...tuozzo.com> wrote:
> >
> > On 7/11/20 7:01 AM, Miklos Szeredi wrote:
> > > On Thu, Jun 25, 2020 at 11:02 AM Vasily Averin <vvs@...tuozzo.com> wrote:
> > >>
> > >> In current implementation fuse_writepages_fill() tries to share the code:
> > >> for new wpa it calls tree_insert() with num_pages = 0
> > >> then switches to common code used non-modified num_pages
> > >> and increments it at the very end.
> > >>
> > >> Though it triggers WARN_ON(!wpa->ia.ap.num_pages) in tree_insert()
> > >>  WARNING: CPU: 1 PID: 17211 at fs/fuse/file.c:1728 tree_insert+0xab/0xc0 [fuse]
> > >>  RIP: 0010:tree_insert+0xab/0xc0 [fuse]
> > >>  Call Trace:
> > >>   fuse_writepages_fill+0x5da/0x6a0 [fuse]
> > >>   write_cache_pages+0x171/0x470
> > >>   fuse_writepages+0x8a/0x100 [fuse]
> > >>   do_writepages+0x43/0xe0
> > >>
> > >> This patch re-works fuse_writepages_fill() to call tree_insert()
> > >> with num_pages = 1 and avoids its subsequent increment and
> > >> an extra spin_lock(&fi->lock) for newly added wpa.
> > >
> > > Looks good.  However, I don't like the way fuse_writepage_in_flight()
> > > is silently changed to insert page into the rb_tree.  Also the
> > > insertion can be merged with the search for in-flight and be done
> > > unconditionally to simplify the logic.  See attached patch.
> >
> > Your patch looks correct for me except 2 things:
>
> Thanks for reviewing.
>
> > 1) you have lost "data->wpa = NULL;" when fuse_writepage_add() returns false.
>
> This is intentional, because this is in the !data->wpa branch.
>
> > 2) in the same case old code did not set data->orig_pages[ap->num_pages] = page;
>
> That is also intentional, in this case the origi_pages[0] is either
> overwritten with the next page or discarded due to data->wpa being
> NULL.
>
> I'll write these up in the patch header.
>

Did you sent out a new version of your patch?
If yes, where can I get it from?

- Sedat -