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From: Michal Hocko <mhocko@suse.com>
To: Vijay Balakrishna <vijayb@linux.microsoft.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Oleg Nesterov <oleg@redhat.com>, Song Liu <songliubraving@fb.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Allen Pais <apais@microsoft.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [v3 1/2] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged
Date: Fri, 25 Sep 2020 09:42:15 +0200	[thread overview]
Message-ID: <20200925074215.GA3389@dhcp22.suse.cz> (raw)
In-Reply-To: <1600305709-2319-2-git-send-email-vijayb@linux.microsoft.com>

On Wed 16-09-20 18:21:48, Vijay Balakrishna wrote:
> When memory is hotplug added or removed the min_free_kbytes must be
> recalculated based on what is expected by khugepaged.  Currently
> after hotplug, min_free_kbytes will be set to a lower default and higher
> default set when THP enabled is lost.  This change restores min_free_kbytes
> as expected for THP consumers.
> 
> Fixes: f000565adb77 ("thp: set recommended min free kbytes")
> 
> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
> Cc: stable@vger.kernel.org
> Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>

I am ok with this patch. I am not sure this is worth backporting to
stable trees becasuse this is not a functional bug. Surprising behavior,
yes, but not much more than that.

Acked-by: Michal Hocko <mhocko@suse.com>

One minor comment below
[...]
> @@ -857,6 +858,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	zone_pcp_update(zone);
>  
>  	init_per_zone_wmark_min();
> +	khugepaged_min_free_kbytes_update();
>  
>  	kswapd_run(nid);
>  	kcompactd_run(nid);
> @@ -1600,6 +1602,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	pgdat_resize_unlock(zone->zone_pgdat, &flags);
>  
>  	init_per_zone_wmark_min();
> +	khugepaged_min_free_kbytes_update();
>  
>  	if (!populated_zone(zone)) {
>  		zone_pcp_reset(zone);

Can we move khugepaged_min_free_kbytes_update into
init_per_zone_wmark_min? If it stays external we might hit the same
problem when somebody else needs to modify min_free_kbytes. Early init
call will be likely too early for khugepaged but that shouldn't matter
AFAICS because it will call khugepaged_min_free_kbytes_update on its
own.
-- 
Michal Hocko
SUSE Labs


  parent reply	other threads:[~2020-09-25  7:42 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-17  1:21 [v3 0/2] recalculate min_free_kbytes post memory hotplug Vijay Balakrishna
2020-09-17  1:21 ` [v3 1/2] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged Vijay Balakrishna
2020-09-23 21:27   ` Vijay Balakrishna
2020-09-25  2:51     ` Andrew Morton
2020-09-25  7:45       ` Michal Hocko
2020-09-25  7:42   ` Michal Hocko [this message]
2020-09-25 16:31     ` Vijay Balakrishna
2020-09-17  1:21 ` [v3 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by user Vijay Balakrishna
2020-09-17  4:22   ` Vijay Balakrishna

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