linux-kernel - Re: [PATCH 01/16] mm/page_alloc: ensure kswapd doesn't accidentally go to sleep

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Message-ID: <ea96d35e-46ae-c168-3186-ddf58ad6806c@arm.com>
Date:   Tue, 13 Sep 2022 12:32:50 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     david@...hat.com, osalvador@...e.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/16] mm/page_alloc: ensure kswapd doesn't accidentally
 go to sleep



On 9/9/22 14:54, Miaohe Lin wrote:
> If ALLOC_KSWAPD is set, wake_all_kswapds() will be called to ensure
> kswapd doesn't accidentally go to sleep. But when reserve_flags is
> set, alloc_flags will be overwritten and ALLOC_KSWAPD is thus lost.
> Preserve the ALLOC_KSWAPD flag in alloc_flags to ensure kswapd won't
> go to sleep accidentally.

Currently wake_all_kswapds() gets skipped subsequently if ALLOC_KSWAPD
is lost, but this only happens when the 'retry:' loops is taken ?

> 
> Fixes: 0a79cdad5eb2 ("mm: use alloc_flags to record if kswapd can wake")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ba5c9402a5cb..4b97a03fa2dd 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5147,7 +5147,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  
>  	reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
>  	if (reserve_flags)
> -		alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, reserve_flags);
> +		alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, reserve_flags) |
> +					  (alloc_flags & ALLOC_KSWAPD);
>  
>  	/*
>  	 * Reset the nodemask and zonelist iterators if memory policies can be