linux-kernel - Re: [PATCH V1] mm: fix bug in some memory information update

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Message-ID: <edigemkxkze3iicku3orrufdadevca33ndqxw2etqvustykpv6@smaext2j3bzp>
Date: Fri, 13 Dec 2024 10:44:15 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: zhouzihan30 <15645113830zzh@...il.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, zhouzihan30 <zhouzihan30@...com>,
        yaowenchao1 <yaowenchao@...com>
Subject: Re: [PATCH V1] mm: fix bug in some memory information update

* zhouzihan30 <15645113830zzh@...il.com> [241213 03:17]:

The subject of this patch is really poor.  "some memory information"?

considering the text below is so much more descriptive, could we have a
meaningful subject?  You will not get the proper people looking at this
without a decent subject.  At least make it "mm/page_alloc" ?

> In the kernel, the zone's lowmem_reserve and _watermark, and the global
> variable 'totalreserve_pages' depend on the value of managed_pages,
> but after running adjust_managed_page_count, these values didn't updated,
> which caused some problems.
> 
> For example, in a system with six 1GB large pages, we found that the value
> of protection in zoneinfo (zone->lowmem_reserve), is not right.
> Its value seems calculated from the initial managed_pages,
> but after the managed_pages changed, was not updated. Only after reading
>  the file /proc/sys/vm/lowmem_reserve_ratio, updates happen.
> 
> read file /proc/sys/vm/lowmem_reserve_ratio:
> 
> lowmem_reserve_ratio_sysctl_handler
> ----setup_per_zone_lowmem_reserve
> --------calculate_totalreserve_pages
> 
> protection changed after reading file:
> 
> [root@...t ~]# cat /proc/zoneinfo | grep protection
>         protection: (0, 2719, 57360, 0)
>         protection: (0, 0, 54640, 0)
>         protection: (0, 0, 0, 0)
>         protection: (0, 0, 0, 0)
> [root@...t ~]# cat /proc/sys/vm/lowmem_reserve_ratio
> 256     256     32      0
> [root@...t ~]# cat /proc/zoneinfo | grep protection
>         protection: (0, 2735, 63524, 0)
>         protection: (0, 0, 60788, 0)
>         protection: (0, 0, 0, 0)
>         protection: (0, 0, 0, 0)
> 
> lowmem_reserve increased also makes the totalreserve_pages increased,
> which causes a decrease in available memory. The one above is just a
>  test machine, and the increase is not significant. On our online machine,
> the reserved memory will increase by several GB due to reading this file.
> It is clearly unreasonable to cause a sharp drop in available memory just
>  by reading a file.
> 
> In this patch, we update reserve memory when update managed_pages, The
> size of reserved memory becomes stable. But it seems that the _watermark
>  should also be updated along with the managed_pages. We have not done
>  it because we are unsure if it is reasonable to set the watermark through
>  the initial managed_pages. If it is not reasonable, we will propose
>  new patch.
> 
> Signed-off-by: zhouzihan30 <zhouzihan30@...com>
> Signed-off-by: yaowenchao1 <yaowenchao@...com>

Who are these people, really?

https://www.kernel.org/doc/html/v6.12/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin

Also, the Signed-off-by doesn't match the sending email (gmail vs
jd.com)?


> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b6958333054d..b23e128afbcd 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5826,10 +5826,13 @@ __meminit void zone_pcp_init(struct zone *zone)
>  			 zone->present_pages, zone_batchsize(zone));
>  }
>  
> +static void setup_per_zone_lowmem_reserve(void);
> +
>  void adjust_managed_page_count(struct page *page, long count)
>  {
>  	atomic_long_add(count, &page_zone(page)->managed_pages);
>  	totalram_pages_add(count);
> +	setup_per_zone_lowmem_reserve();
>  }
>  EXPORT_SYMBOL(adjust_managed_page_count);
>  
> -- 
> 2.33.0
> 
>