linux-kernel - Re: [PATCH 00/10] cleanup vma_merge() and improve mergeability tests

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Date:   Mon, 20 Mar 2023 10:16:21 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        maple-tree@...ts.infradead.org
Subject: Re: [PATCH 00/10] cleanup vma_merge() and improve mergeability tests


Sorry for the late review, I've been away.

For the whole series,
Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

* Vlastimil Babka <vbabka@...e.cz> [230309 06:18]:
> Also available in git:
> https://git.kernel.org/vbabka/h/vma_merge_cleanup-v1r2
> 
> Changes since RFC:
> - rebased to 6.3-rc1, dropped first patch (urgent fix) that was merged there
> - reindent parameters of mergeability checks (suggested by willy on IRC)
> 
> My initial goal here was to try making the check for vm_ops->close in
> is_mergeable_vma() only be applied for vma's that would be truly removed
> as part of the merge (see Patch 9). This would then allow reverting the
> quick fix d014cd7c1c35 ("mm, mremap: fix mremap() expanding for vma's
> with vm_ops->close()"). This was successful enough to allow the revert
> (Patch 10). Checks using can_vma_merge_before() are still pessimistic
> about possible vma removal, and making them precise would probably
> complicate the vma_merge() code too much.
> 
> Liam's 6.3-rc1 simplification of vma_merge() and removal of
> __vma_adjust() was very much helpful in understanding the vma_merge()
> implementation and especially when vma removals can happen, which is now
> very obvious. While studing the code, I've found ways to make it
> hopefully even more easy to follow, so that's the patches 1-8. That made
> me also notice a bug that's now already fixed in 6.3-rc1.
> 
> Vlastimil Babka (10):
>   mm/mmap/vma_merge: use only primary pointers for preparing merge
>   mm/mmap/vma_merge: use the proper vma pointer in case 3
>   mm/mmap/vma_merge: use the proper vma pointers in cases 1 and 6
>   mm/mmap/vma_merge: use the proper vma pointer in case 4
>   mm/mmap/vma_merge: initialize mid and next in natural order
>   mm/mmap/vma_merge: set mid to NULL if not applicable
>   mm/mmap/vma_merge: rename adj_next to adj_start
>   mm/mmap/vma_merge: convert mergeability checks to return bool
>   mm/mmap: start distinguishing if vma can be removed in mergeability
>     test
>   mm/mremap: simplify vma expansion again
> 
>  mm/mmap.c   | 142 ++++++++++++++++++++++++++++------------------------
>  mm/mremap.c |  20 ++------
>  2 files changed, 80 insertions(+), 82 deletions(-)
> 
> -- 
> 2.39.2
>