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

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Date:   Mon, 25 Oct 2021 16:56:28 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     NeilBrown <neilb@...e.de>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Dave Chinner <david@...morbit.com>,
        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 Mon 25-10-21 16:30:23, Uladzislau Rezki wrote:
> >
> > I would really prefer if this was not the main point of arguing here.
> > Unless you feel strongly about msleep I would go with schedule_timeout
> > here because this is a more widely used interface in the mm code and
> > also because I feel like that relying on the rounding behavior is just
> > subtle. Here is what I have staged now.
> >
> I have a preference but do not have a strong opinion here. You can go
> either way you want.
> 
> >
> > Are there any other concerns you see with this or other patches in the
> > series?
> >
> it is better if you could send a new vX version because it is hard to
> combine every "folded"

Yeah, I plan to soon. I just wanted to sort out most things before
spaming with a new version.

> into one solid commit. One comment below:
> 
> > ---
> > commit c1a7e40e6b56fed5b9e716de7055b77ea29d89d0
> > Author: Michal Hocko <mhocko@...e.com>
> > Date:   Wed Oct 20 10:12:45 2021 +0200
> >
> >     fold me "mm/vmalloc: add support for __GFP_NOFAIL"
> >
> >     Add a short sleep before retrying. 1 jiffy is a completely random
> >     timeout. Ideally the retry would wait for an explicit event - e.g.
> >     a change to the vmalloc space change if the failure was caused by
> >     the space fragmentation or depletion. But there are multiple different
> >     reasons to retry and this could become much more complex. Keep the retry
> >     simple for now and just sleep to prevent from hogging CPUs.
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 0fb5413d9239..a866db0c9c31 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2944,6 +2944,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> >         do {
> >                 ret = vmap_pages_range(addr, addr + size, prot, area->pages,
> >                         page_shift);
> > +               schedule_timeout_uninterruptible(1);
> >
> We do not want to schedule_timeout_uninterruptible(1); every time.
> Only when an error is detected.

Because I was obviously in a brainless mode when doing that one. Thanks
for pointing this out!
-- 
Michal Hocko
SUSE Labs