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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Thu, 21 Oct 2021 12:40:38 +0200
To:     Michal Hocko <mhocko@suse.com>, NeilBrown <neilb@suse.de>
Cc:     NeilBrown <neilb@suse.de>, Uladzislau Rezki <urezki@gmail.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
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> On Thu 21-10-21 21:13:35, Neil Brown wrote:
> > 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 the 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_timeout(1)
> > > > 
> > > 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 = 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.
> 
> That was my thinking as well. Not to mention jiffies_to_msecs just to do
> msecs_to_jiffies right after which seems like a pointless wasting of
> cpu cycle. But maybe I was missing some other reasons why msleep would
> be superior.
>

To me the msleep is just more simpler from semantic point of view, i.e.
it is as straight forward as it can be. In case of interruptable/uninteraptable
sleep it can be more confusing for people.

When it comes to rounding and possibility to sleep more than 1 tick, it
really does not matter here, we do not need to guarantee exact sleeping
time.

Therefore i proposed to switch to the msleep().

--
Vlad Rezki