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

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Message-ID: <20201214140337.GD32193@dhcp22.suse.cz>
Date:   Mon, 14 Dec 2020 15:03:37 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, vbabka@...e.cz, david@...hat.com,
        osalvador@...e.de, dan.j.williams@...el.com, sashal@...nel.org,
        tyhicks@...ux.microsoft.com, iamjoonsoo.kim@....com,
        mike.kravetz@...cle.com, rostedt@...dmis.org, mingo@...hat.com,
        jgg@...pe.ca, peterz@...radead.org, mgorman@...e.de,
        willy@...radead.org, rientjes@...gle.com, jhubbard@...dia.com,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 2/6] mm cma: rename PF_MEMALLOC_NOCMA to
 PF_MEMALLOC_PIN

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>

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.
-- 
Michal Hocko
SUSE Labs