linux-kernel - Re: [PATCH v2] memcg: page_alloc: skip bulk allocator for __GFP

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Message-ID: <YWhNom2T+codyPea@dhcp22.suse.cz>
Date:   Thu, 14 Oct 2021 17:32:50 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Uladzislau Rezki <urezki@...il.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Roman Gushchin <guro@...com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] memcg: page_alloc: skip bulk allocator for
 __GFP_ACCOUNT

On Thu 14-10-21 08:16:07, Shakeel Butt wrote:
> The commit 5c1f4e690eec ("mm/vmalloc: switch to bulk allocator in
> __vmalloc_area_node()") switched to bulk page allocator for order 0
> allocation backing vmalloc. However bulk page allocator does not support
> __GFP_ACCOUNT allocations and there are several users of
> kvmalloc(__GFP_ACCOUNT).
> 
> For now make __GFP_ACCOUNT allocations bypass bulk page allocator. In

I would go with
For now make __GFP_ACCOUNT allocations bypass the fast path of the bulk
allocator and make it fallback to the regular page allocator as if the
former failed.

> future if there is workload that can be significantly improved with the
> bulk page allocator with __GFP_ACCCOUNT support, we can revisit the
> decision.
> 
> Fixes: 5c1f4e690eec ("mm/vmalloc: switch to bulk allocator in __vmalloc_area_node()")
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>

Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!

> ---
> Changes since v1:
> - do fallback allocation instead of failure, suggested by Michal Hocko.
> - Added memcg_kmem_enabled() check, corrected by Vasily Averin
> 
>  mm/page_alloc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 668edb16446a..9ca871dc8602 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5230,6 +5230,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>  	if (unlikely(page_array && nr_pages - nr_populated == 0))
>  		goto out;
>  
> +	/* Bulk allocator does not support memcg accounting. */
> +	if (memcg_kmem_enabled() && (gfp & __GFP_ACCOUNT))
> +		goto failed;
> +
>  	/* Use the single page allocator for one page. */
>  	if (nr_pages - nr_populated == 1)
>  		goto failed;
> -- 
> 2.33.0.882.g93a45727a2-goog

-- 
Michal Hocko
SUSE Labs