Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 2 Mar 2022 10:24:15 +0100
From:   Jan Kara <jack@suse.cz>
To:     Richard Weinberger <richard@nod.at>
Cc:     Jan Kara <jack@suse.cz>, wuchi zero <wuchi.zero@gmail.com>,
        =?utf-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>,
        tj <tj@kernel.org>, mszeredi <mszeredi@redhat.com>,
        sedat dilek <sedat.dilek@gmail.com>, axboe <axboe@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        torvalds <torvalds@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Different writeback timing since v5.14
Message-ID: <20220302092415.4sikhzup7sorhxgy@quack3.lan>
References: <2104629126.100059.1646129517209.JavaMail.zimbra@nod.at>
 <20220301103218.ulbmakdy4gbw2fso@quack3.lan>
 <719960584.100772.1646147154879.JavaMail.zimbra@nod.at>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <719960584.100772.1646147154879.JavaMail.zimbra@nod.at>
Precedence: bulk

On Tue 01-03-22 16:05:54, Richard Weinberger wrote:
> Jan,
> 
> ----- Urspr?ngliche Mail -----
> > Von: "Jan Kara" <jack@suse.cz>
> >> Is this expected?
> >> Just want to make sure that the said commit didn't uncover an UBIFS issue.
> > 
> > Yes, I think it is expected. Likely the background threshold for UBIFS bdi
> > is very small (probably UBIFS is not used much for writeback compared to
> > other filesystems). Previously, we just used wb_stat() which returned 0
> > (PCP counter inexact value) and so background writeback didn't trigger. Now
> > we use wb_stat_sum() when threshold is small, get exact value of dirty
> > pages and decide to start background writeback.
> 
> Thanks for the prompt reply!
> 
> > The only thing is, whether it is really expected that the threshold for
> > UBIFS bdi is so small. You can check the values in
> > /sys/kernel/debug/bdi/<bdi>/stats.
> 
> BdiDirtyThresh is indeed 0.
> 
> BdiWriteback:                0 kB
> BdiReclaimable:              0 kB
> BdiDirtyThresh:              0 kB
> DirtyThresh:            772620 kB
> BackgroundThresh:       385836 kB
> BdiDirtied:                  0 kB
> BdiWritten:                  0 kB
> BdiWriteBandwidth:      102400 kBps
> b_dirty:                     0
> b_io:                        0
> b_more_io:                   0
> b_dirty_time:                0
> bdi_list:                    1
> state:                       1

Yes, so this looks expected given the BDI wasn't active yet at all...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR