linux-kernel - Re: [PATCH v3] ksm: use range-walk function to jump over holes in scan_get_next_rmap

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Message-ID: <05d7832e-7bbc-4c73-b293-f512b4776aeb@redhat.com>
Date: Fri, 17 Oct 2025 17:44:33 +0200
From: David Hildenbrand <david@...hat.com>
To: Pedro Demarchi Gomes <pedrodemargomes@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Xu Xin <xu.xin16@....com.cn>, craftfever <craftfever@...mail.cc>,
 Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ksm: use range-walk function to jump over holes in
 scan_get_next_rmap_item

On 16.10.25 03:22, Pedro Demarchi Gomes wrote:
> Currently, scan_get_next_rmap_item() walks every page address in a VMA
> to locate mergeable pages. This becomes highly inefficient when scanning
> large virtual memory areas that contain mostly unmapped regions.
> 
> This patch replaces the per-address lookup with a range walk using
> walk_page_range(). The range walker allows KSM to skip over entire
> unmapped holes in a VMA, avoiding unnecessary lookups.
> This problem was previously discussed in [1].
> 
> [1] https://lore.kernel.org/linux-mm/423de7a3-1c62-4e72-8e79-19a6413e420c@redhat.com/
> 
> ---
> 
> v3:
>    - Treat THPs in ksm_pmd_entry
>    - Update ksm_scan.address outside walk_page_range
>    - Change goto to while loop
> 
> v2: https://lore.kernel.org/all/20251014151126.87589-1-pedrodemargomes@gmail.com/
>    - Use pmd_entry to walk page range
>    - Use cond_resched inside pmd_entry()
>    - walk_page_range returns page+folio
> 
> v1: https://lore.kernel.org/all/20251014055828.124522-1-pedrodemargomes@gmail.com/
> 
> Reported-by: craftfever <craftfever@...mail.cc>
> Closes: https://lkml.kernel.org/r/020cf8de6e773bb78ba7614ef250129f11a63781@murena.io
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@...il.com>
> ---

This patch will need some more work.

@Andrew, please drop it for now.

-- 
Cheers

David / dhildenb