linux-kernel - Re: [v3 2/2] mm: khugepaged: avoid overriding min_free

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Date:   Wed, 16 Sep 2020 21:22:06 -0700
From:   Vijay Balakrishna <vijayb@...ux.microsoft.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Song Liu <songliubraving@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Michal Hocko <mhocko@...e.com>,
        Allen Pais <apais@...rosoft.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [v3 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by
 user

Please ignore this patch.  I forgot to run scripts/checkpatch.pl and see

CHECK: Alignment should match open parenthesis
#30: FILE: mm/khugepaged.c:2287:
+       if (recommended_min > min_free_kbytes ||
+               recommended_min > user_min_free_kbytes) {

ERROR: do not initialise globals to 0
#43: FILE: mm/page_alloc.c:318:
+int user_min_free_kbytes = 0;

Sorry for trouble, I will send a new version.

Vijay

On 9/16/2020 6:21 PM, Vijay Balakrishna wrote:
> set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
> user.  Post start-of-day THP enable or memory hotplug operations can
> lose user specified min_free_kbytes, in particular when it is higher than
> calculated recommended value.  user_min_free_kbytes initialized to 0
> to avoid undesired result when comparing with  "unsigned long" type.
> 
> Signed-off-by: Vijay Balakrishna <vijayb@...ux.microsoft.com>
> Cc: stable@...r.kernel.org
> Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>
> ---
>   mm/khugepaged.c | 3 ++-
>   mm/page_alloc.c | 2 +-
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 4f7107476a6f..3c1147816d12 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2283,7 +2283,8 @@ static void set_recommended_min_free_kbytes(void)
>   			      (unsigned long) nr_free_buffer_pages() / 20);
>   	recommended_min <<= (PAGE_SHIFT-10);
>   
> -	if (recommended_min > min_free_kbytes) {
> +	if (recommended_min > min_free_kbytes ||
> +		recommended_min > user_min_free_kbytes) {
>   		if (user_min_free_kbytes >= 0)
>   			pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
>   				min_free_kbytes, recommended_min);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fab5e97dc9ca..7b81fb139034 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -315,7 +315,7 @@ compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
>   };
>   
>   int min_free_kbytes = 1024;
> -int user_min_free_kbytes = -1;
> +int user_min_free_kbytes = 0;
>   #ifdef CONFIG_DISCONTIGMEM
>   /*
>    * DiscontigMem defines memory ranges as separate pg_data_t even if the ranges
>