Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <916aedc8-1d0b-a0f9-5ddf-6c6305e7cbdb@redhat.com>
Date:   Mon, 16 Jan 2023 11:53:00 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.0
Subject: Re: [PATCH v3] mm/page_ext: Do not allocate space for page_ext->flags
 if not needed
Content-Language: en-US
To:     Vlastimil Babka <vbabka@suse.cz>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        akpm@linux-foundation.org, mhocko@suse.com,
        quic_charante@quicinc.com, lizhe.67@bytedance.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Mike Rapoport <rppt@linux.ibm.com>
References: <20230113154253.92480-1-pasha.tatashin@soleen.com>
 <0c706897-b2cc-714c-c72e-4154b1f3f52b@suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <0c706897-b2cc-714c-c72e-4154b1f3f52b@suse.cz>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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@soleen.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> Mike's comments look reasonable to me.

Seconded

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

-- 
Thanks,

David / dhildenb