linux-kernel - Re: [PATCH v3 2/6] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC

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Date:   Mon, 14 Dec 2020 23:37:55 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, mike.kravetz@...cle.com,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_PIN

On Mon, Dec 14, 2020 at 9:03 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Fri 11-12-20 15:21:36, Pavel Tatashin wrote:
> > PF_MEMALLOC_NOCMA is used ot guarantee that the allocator will not return
> > pages that might belong to CMA region. This is currently used for long
> > term gup to make sure that such pins are not going to be done on any CMA
> > pages.
> >
> > When PF_MEMALLOC_NOCMA has been introduced we haven't realized that it is
> > focusing on CMA pages too much and that there is larger class of pages that
> > need the same treatment. MOVABLE zone cannot contain any long term pins as
> > well so it makes sense to reuse and redefine this flag for that usecase as
> > well. Rename the flag to PF_MEMALLOC_PIN which defines an allocation
> > context which can only get pages suitable for long-term pins.
> >
> > Also re-name:
> > memalloc_nocma_save()/memalloc_nocma_restore
> > to
> > memalloc_pin_save()/memalloc_pin_restore()
> > and make the new functions common.
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> > Reviewed-by: John Hubbard <jhubbard@...dia.com>
>
> Acked-by: Michal Hocko <mhocko@...e.com>

Thank you.

>
> with one comment below
> [...]
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1576,7 +1576,7 @@ extern struct pid *cad_pid;
> >  #define PF_SWAPWRITE         0x00800000      /* Allowed to write to swap */
> >  #define PF_NO_SETAFFINITY    0x04000000      /* Userland is not allowed to meddle with cpus_mask */
> >  #define PF_MCE_EARLY         0x08000000      /* Early kill for mce process policy */
> > -#define PF_MEMALLOC_NOCMA    0x10000000      /* All allocation request will have _GFP_MOVABLE cleared */
> > +#define PF_MEMALLOC_PIN              0x10000000      /* All allocation request will have _GFP_MOVABLE cleared */
>
> This comment is not really helpeful. I would go with
> /* Allocation context constrained to zones which allow long term
>  * pinning.
>  */
>
> Something similar would be useful for memalloc_pin* functions as well.

I will add it.

> --
> Michal Hocko
> SUSE Labs