linux-kernel - Re: [PATCH v3] mm/page_ext: Do not allocate space for page

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Date:   Mon, 16 Jan 2023 11:53:00 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        akpm@...ux-foundation.org, mhocko@...e.com,
        quic_charante@...cinc.com, lizhe.67@...edance.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH v3] mm/page_ext: Do not allocate space for page_ext->flags
 if not needed

On 16.01.23 11:51, Vlastimil Babka wrote:
> On 1/13/23 16:42, Pasha Tatashin wrote:
>> There is 8 byte page_ext->flags field allocated per page whenever
>> CONFIG_PAGE_EXTENSION is enabled. However, not every user of page_ext
>> uses flags. Therefore, check whether flags is needed at least by one
>> user and if so allocate space for it.
>>
>> For example when page_table_check is enabled, on a machine with 128G
>> of memory before the fix:
>>
>> [    2.244288] allocated 536870912 bytes of page_ext
>> after the fix:
>> [    2.160154] allocated 268435456 bytes of page_ext
>>
>> Also, add a comment before page_ext_operations that describes the
>> field, and remove check if need() is set, as that is now a required
>> field.
>>
>> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Mike's comments look reasonable to me.

Seconded

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb