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

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Message-ID: <YWdXv+RBjXvdmsK+@carbon.DHCP.thefacebook.com>
Date:   Wed, 13 Oct 2021 15:03:43 -0700
From:   Roman Gushchin <guro@...com>
To:     Shakeel Butt <shakeelb@...gle.com>
CC:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Uladzislau Rezki <urezki@...il.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: page_alloc: skip bulk allocator for __GFP_ACCOUNT

On Wed, Oct 13, 2021 at 12:43:38PM -0700, 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
> 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>
> ---
>  mm/page_alloc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 668edb16446a..b3acad4615d3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5215,6 +5215,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>  	unsigned int alloc_flags = ALLOC_WMARK_LOW;
>  	int nr_populated = 0, nr_account = 0;
>  
> +	/* Bulk allocator does not support memcg accounting. */
> +	if (unlikely(gfp & __GFP_ACCOUNT))
> +		goto out;
> +

Isn't it a bit too aggressive?

How about
    if (WARN_ON_ONCE(gfp & __GFP_ACCOUNT))
       gfp &= ~__GFP_ACCOUNT;

And maybe with some explanatory message?

Thanks!