linux-kernel - Re: [RFC 2/3] mm/vmalloc: add support for __GFP

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Date:   Wed, 20 Oct 2021 16:29:14 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>
Subject: Re: [RFC 2/3] mm/vmalloc: add support for __GFP_NOFAIL

On Wed, Oct 20, 2021 at 4:06 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Wed 20-10-21 15:54:23, Uladzislau Rezki wrote:
> > > > >
> > > > I think adding kind of schedule() will not make things worse and in corner
> > > > cases could prevent a power drain by CPU. It is important for mobile devices.
> > >
> > > I suspect you mean schedule_timeout here? Or cond_resched? I went with a
> > > later for now, I do not have a good idea for how to long to sleep here.
> > > I am more than happy to change to to a sleep though.
> > >
> > cond_resched() reschedules only if TIF_NEED_RESCHED is raised what is not good
> > here. Because in our case we know that we definitely would like to
> > take a breath. Therefore
> > invoking the schedule() is more suitable here. It will give a CPU time
> > to another waiting
> > process(if exists) in any case putting the "current" one to the tail.
>
> Yes, but there is no explicit event to wait for currently.
>
> > As for adding a delay. I am not sure about for how long to delay or i
> > would say i do not
> > see a good explanation why for example we delay for 10 milliseconds or so.
>
> 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.

-- 
Uladzislau Rezki