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From:   "NeilBrown" <neilb@suse.de>
To:     "Uladzislau Rezki" <urezki@gmail.com>
Cc:     "Michal Hocko" <mhocko@suse.com>, "Michal Hocko" <mhocko@suse.com>,
        "Linux Memory Management List" <linux-mm@kvack.org>,
        "Dave Chinner" <david@fromorbit.com>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        "Christoph Hellwig" <hch@infradead.org>,
        linux-fsdevel@vger.kernel.org,
        "LKML" <linux-kernel@vger.kernel.org>,
        "Ilya Dryomov" <idryomov@gmail.com>,
        "Jeff Layton" <jlayton@kernel.org>
Subject: Re: [RFC 2/3] mm/vmalloc: add support for __GFP_NOFAIL
In-reply-to: <20211020192430.GA1861@pc638.lan>
References: <20211018114712.9802-3-mhocko@kernel.org>,
 <20211019110649.GA1933@pc638.lan>, <YW6xZ7vi/7NVzRH5@dhcp22.suse.cz>,
 <20211019194658.GA1787@pc638.lan>, <YW/SYl/ZKp7W60mg@dhcp22.suse.cz>,
 <CA+KHdyUopXQVTp2=X-7DYYFNiuTrh25opiUOd1CXED1UXY2Fhg@mail.gmail.com>,
 <YXAiZdvk8CGvZCIM@dhcp22.suse.cz>,
 <CA+KHdyUyObf2m51uFpVd_tVCmQyn_mjMO0hYP+L0AmRs0PWKow@mail.gmail.com>,
 <YXAtYGLv/k+j6etV@dhcp22.suse.cz>,
 <CA+KHdyVdrfLPNJESEYzxfF+bksFpKGCd8vH=NqdwfPOLV9ZO8Q@mail.gmail.com>,
 <20211020192430.GA1861@pc638.lan>
Date:   Thu, 21 Oct 2021 21:13:35 +1100
Message-id: <163481121586.17149.4002493290882319236@noble.neil.brown.name>
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On Thu, 21 Oct 2021, Uladzislau Rezki wrote:
> On Wed, Oct 20, 2021 at 05:00:28PM +0200, Uladzislau Rezki wrote:
> > >
> > > On Wed 20-10-21 16:29:14, Uladzislau Rezki wrote:
> > > > On Wed, Oct 20, 2021 at 4:06 PM Michal Hocko <mhocko@suse.com> wrote:
> > > [...]
> > > > > As I've said I am OK with either of the two. Do you or anybody have=
 any
> > > > > preference? Without any explicit event to wake up for neither of th=
e two
> > > > > is more than just an optimistic retry.
> > > > >
> > > > From power perspective it is better to have a delay, so i tend to say
> > > > that delay is better.
> > >
> > > I am a terrible random number generator. Can you give me a number
> > > please?
> > >
> > Well, we can start from one jiffy so it is one timer tick: schedule_timeo=
ut(1)
> >=20
> A small nit, it is better to replace it by the simple msleep() call: msleep=
(jiffies_to_msecs(1));

I disagree.  I think schedule_timeout_uninterruptible(1) is the best
wait to sleep for 1 ticl

msleep() contains
  timeout =3D msecs_to_jiffies(msecs) + 1;
and both jiffies_to_msecs and msecs_to_jiffies might round up too.
So you will sleep for at least twice as long as you asked for, possible
more.

NeilBrown


>=20
> --
> Vlad Rezki
>=20
>=20