linux-kernel - Re: [PATCH v4] mm/page_ext: Do not allocate space for page

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Message-ID: <59557eaf-7301-d142-4549-c3e196d011d5@google.com>
Date:   Tue, 17 Jan 2023 21:56:36 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
cc:     rppt@...nel.org, akpm@...ux-foundation.org, mhocko@...e.com,
        vbabka@...e.cz, david@...hat.com, quic_charante@...cinc.com,
        lizhe.67@...edance.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4] mm/page_ext: Do not allocate space for page_ext->flags
 if not needed

On Tue, 17 Jan 2023, 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 kernel-doc comment before page_ext_operations that describes
> the fields, 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>
> Acked-by: David Hildenbrand <david@...hat.com>

Acked-by: David Rientjes <rientjes@...gle.com>