linux-kernel - Re: [PATCH v2 6/7] mm: Batch around can_change_pte

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Message-ID: <bbd0e5fb-ad47-4531-adde-c2c2ee2cef61@redhat.com>
Date: Tue, 29 Apr 2025 11:15:42 +0200
From: David Hildenbrand <david@...hat.com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org
Cc: ryan.roberts@....com, willy@...radead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, catalin.marinas@....com, will@...nel.org,
 Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
 jannh@...gle.com, anshuman.khandual@....com, peterx@...hat.com,
 joey.gouly@....com, ioworker0@...il.com, baohua@...nel.org,
 kevin.brodsky@....com, quic_zhenhuah@...cinc.com,
 christophe.leroy@...roup.eu, yangyicong@...ilicon.com,
 linux-arm-kernel@...ts.infradead.org, namit@...are.com, hughd@...gle.com,
 yang@...amperecomputing.com, ziy@...dia.com
Subject: Re: [PATCH v2 6/7] mm: Batch around can_change_pte_writable()

On 29.04.25 07:23, Dev Jain wrote:
> In preparation for patch 7, we need to properly batch around
> can_change_pte_writable(). We batch around pte_needs_soft_dirty_wp() by
> the corresponding fpb flag, we batch around the page-anon exclusive check
> using folio_maybe_mapped_shared(); modify_prot_start_ptes() collects the
> dirty and access bits across the batch, therefore batching across
> pte_dirty(): this is correct since the dirty bit on the PTE really
> is just an indication that the folio got written to, so even if
> the PTE is not actually dirty (but one of the PTEs in the batch is),
> the wp-fault optimization can be made.

If you want to add a batched version of can_change_pte_writable(), do it 
right away instead of just adding parameters to functions.

Then, add a simple

#define can_change_pte_writable(...) can_change_ptes_writable(..., 1);

So you don't have to touch all callers and don't have to update the 
function name in comments.

-- 
Cheers,

David / dhildenb