linux-kernel - Re: [PATCH v2 0/5] madvise cleanup

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Message-ID: <a380ee77-bbbe-4b3b-b623-21fdfa4e8d28@lucifer.local>
Date: Fri, 20 Jun 2025 18:33:26 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
        Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Lance Yang <ioworker0@...il.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v2 0/5] madvise cleanup

On Fri, Jun 20, 2025 at 10:21:08AM -0700, SeongJae Park wrote:
> On Fri, 20 Jun 2025 16:33:00 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>
> > This is a series of patches that helps address a number of historic
> > problems in the madvise() implementation:
> >
> > * Eliminate the visitor pattern and having the code which is implemented
> >   for both the anon_vma_name implementation and ordinary madvise()
> >   operations use the same madvise_vma_behavior() implementation.
> >
> > * Thread state through the madvise_behavior state object - this object,
> >   very usefully introduced by SJ, is already used to transmit state through
> >   operations. This series extends this by having all madvise() operations
> >   use this, including anon_vma_name.
> >
> > * Thread range, VMA state through madvise_behavior - This helps avoid a lot
> >   of the confusing code around range and VMA state and again keeps things
> >   consistent and with a single 'source of truth'.
> >
> > * Addressing the very strange behaviour around the passed around struct
> >   vm_area_struct **prev pointer - all read-only users do absolutely nothing
> >   with the prev pointer. The only function that uses it is
> >   madvise_update_vma(), and in all cases prev is always reset to
> >   VMA.
> >
> >   Fix this by no longer having aything but madvise_update_vma() reference
> >   prev, and having madvise_walk_vmas() update prev in each
> >   instance. Additionally make it clear that the meaningful change in vma
> >   state is when madvise_update_vma() potentially merges a VMA, so
> >   explicitly retrieve the VMA in this case.
> >
> > * Update and clarify the madvise_walk_vmas() function - this is a source of
> >   a great deal of confusion, so simplify, stop using prev = NULL to signify
> >   that the mmap lock has been dropped (!) and make that explicit, and add
> >   some comments to explain what's going on.
> >
> > v2:
> > * Propagated tags (thanks everyone!)
> > * Don't separate out __MADV_SET_ANON_VMA_NAME and __MADV_SET_CLEAR_VMA_NAME,
>
> FWIW.  If this cover letter is added to the first patch, like Andrew usually
> does, as-is, checkpatch.pl may warn like below.
>
>    WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
>
> Obviously no real problem and I don't really care.  I just found this since my
> tool (hkml) runs checkpatch.pl after adding the cover letter to the first
> patch, and hence this is just FWIW.

Yeah, sorry, this is because I didn't 'compress' the v2 revision log, which
won't be reproduced in patches anyway so should be ok :>)

>
>
> Thanks,
> SJ
>
> [...]