linux-kernel - RE:(2) [PATCH] page_alloc: avoid the negative free for meminfo available

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Message-ID: <20230103082008epcms1p6f75b54cbfeba0a1ab9a8044dc650134b@epcms1p6>
Date:   Tue, 03 Jan 2023 17:20:08 +0900
From:   김재원 <jaewon31.kim@...sung.com>
To:     Michal Hocko <mhocko@...e.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jaewon31.kim@...il.com" <jaewon31.kim@...il.com>
Subject: RE:(2) [PATCH] page_alloc: avoid the negative free for meminfo
 available

>On Tue 03-01-23 16:28:07, Jaewon Kim wrote:
>> The totalreserve_pages could be higher than the free because of
>> watermark high or watermark boost. Handle this situation and fix it to 0
>> free size.
>
>What is the actual problem you are trying to address by this change?

Hello

As described on the original commit,
  34e431b0ae39 /proc/meminfo: provide estimated available memory
mm is tring to provide the avaiable memory to user space.

But if free is negative, the available memory shown to userspace
would be shown smaller thatn the actual available size. The userspace
may do unwanted memory shrinking actions like process kills.

I think the logic sholud account the positive size only.

BR

>
>> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
>> ---
>>  mm/page_alloc.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 218b28ee49ed..e510ae83d5f3 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5948,6 +5948,8 @@ long si_mem_available(void)
>>  	 * without causing swapping or OOM.
>>  	 */
>>  	available = global_zone_page_state(NR_FREE_PAGES) - totalreserve_pages;
>> +	if (available < 0)
>> +		available = 0;
>>  
>>  	/*
>>  	 * Not all the page cache can be freed, otherwise the system will
>> -- 
>> 2.17.1
>
>-- 
>Michal Hocko
>SUSE Labs



 
--------- Original Message ---------
Sender : Michal Hocko <mhocko@...e.com>
Date : 2023-01-03 17:03 (GMT+9)
Title : Re: [PATCH] page_alloc: avoid the negative free for meminfo available
 
On Tue 03-01-23 16:28:07, Jaewon Kim wrote:
> The totalreserve_pages could be higher than the free because of
> watermark high or watermark boost. Handle this situation and fix it to 0
> free size.

What is the actual problem you are trying to address by this change?

> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
> ---
>  mm/page_alloc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 218b28ee49ed..e510ae83d5f3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5948,6 +5948,8 @@ long si_mem_available(void)
>           * without causing swapping or OOM.
>           */
>          available = global_zone_page_state(NR_FREE_PAGES) - totalreserve_pages;
> +        if (available < 0)
> +                available = 0;
>  
>          /*
>           * Not all the page cache can be freed, otherwise the system will
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs