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Tue, 11 May 2021 03:01:27 -0700 (PDT) MIME-Version: 1.0 References: <20210511052626.19005-1-wuchi.zero@gmail.com> <20210511090632.GH24154@quack2.suse.cz> In-Reply-To: <20210511090632.GH24154@quack2.suse.cz> From: chi wu Date: Tue, 11 May 2021 18:01:17 +0800 Message-ID: Subject: Re: [PATCH] mm/page-writeback: Update the comment of Dirty position control To: Jan Kara Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, tj@kernel.org, Miklos Szeredi , sedat.dilek@gmail.com, Jens Axboe , Howard Cochran Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 70B34D5 Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=qTaNv7GO; spf=pass (imf29.hostedemail.com: domain of wuchizero@gmail.com designates 209.85.210.182 as permitted sender) smtp.mailfrom=wuchizero@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam04 X-Stat-Signature: fs5ne67cagemihn1grwdpx3otqjhfs1j Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=mail-pf1-f182.google.com; client-ip=209.85.210.182 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620727282-928964 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Jan Kara =E4=BA=8E2021=E5=B9=B45=E6=9C=8811=E6=97=A5=E5=91= =A8=E4=BA=8C =E4=B8=8B=E5=8D=885:06=E5=86=99=E9=81=93=EF=BC=9A > > On Tue 11-05-21 13:26:26, Chi Wu wrote: > > As the value of pos_ratio_polynom() clamp between 0 and > > 2LL << RATELIMIT_CALC_SHIFT, the global control line should be > > consistent with it. > > > > Signed-off-by: Chi Wu > > --- > > mm/page-writeback.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > index 0062d5c57d41..e9a4f6cf12bb 100644 > > --- a/mm/page-writeback.c > > +++ b/mm/page-writeback.c > > @@ -845,7 +845,7 @@ static long long pos_ratio_polynom(unsigned long se= tpoint, > > * ^ pos_ratio > > * | > > * | |<=3D=3D=3D=3D=3D global dirty control scope =3D= =3D=3D=3D=3D=3D>| > > - * 2.0 .............* > > + * 2.0 * * * * * * * > > * | .* > > * | . * > > * | . * > > Generally, pos_ratio is used only within [freerun, limit] range so its > values outside of that range don't matter much. But you're right that Thanks. Yes, most time it is. As the follow code and in the "dtc->wb_dirty < 8" rampup case, dirty pages may break the rules. . . . . if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { long long wb_pos_ratio; if (dtc->wb_dirty < 8) { dtc->pos_ratio =3D min_t(long long, pos_ratio * 2, 2 << RATELIMIT_CALC_SHIFT); return; } if (dtc->wb_dirty >=3D wb_thresh) return; . . . > pos_ratio_polynom() clamps the computed value as you describe and we can > visualize that in the graph as well. Just please move the '*' line you ad= d > by one space to the right so that the curve really follows the cubic curv= e > upto 'freerun' mark (the vertical '.' line). Thanks.I'll correct it later. > > Honza > -- > Jan Kara > SUSE Labs, CR