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Message-Id: <20241111161102.e047bce4adfbf38002b7a9cf@linux-foundation.org>
Date: Mon, 11 Nov 2024 16:11:02 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: willy@...radead.org, liam.howlett@...cle.com,
 lorenzo.stoakes@...cle.com, mhocko@...e.com, vbabka@...e.cz,
 hannes@...xchg.org, mjguzik@...il.com, oliver.sang@...el.com,
 mgorman@...hsingularity.net, david@...hat.com, peterx@...hat.com,
 oleg@...hat.com, paulmck@...nel.org, brauner@...nel.org,
 dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com,
 minchan@...gle.com, jannh@...gle.com, shakeel.butt@...ux.dev,
 souravpanda@...gle.com, pasha.tatashin@...een.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 0/4] move per-vma lock into vm_area_struct

On Mon, 11 Nov 2024 15:19:22 -0800 Suren Baghdasaryan <surenb@...gle.com> wrote:

> On Mon, Nov 11, 2024 at 2:18 PM Davidlohr Bueso <dave@...olabs.net> wrote:
> >
> > On Mon, 11 Nov 2024, Suren Baghdasaryan wrote:
> >
> > >To minimize memory overhead, vm_lock implementation is changed from
> > >using rw_semaphore (40 bytes) to an atomic (8 bytes) and several
> > >vm_area_struct members are moved into the last cacheline, resulting
> > >in a less fragmented structure:
> >
> > I am not a fan of building a custom lock, replacing a standard one.
> 
> Understandable.

If we're going to invent a new lock type, I'm thinking we should do
that - make it a standaline thing, add full lockdep support, etc.

I wonder if we could remove the lock from the vma altogeher and use an
old-fashioned hashed lock.  An array of locks indexed by the vma
address.  It might work well enough, although sizing the array would be
difficult.


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