linux-kernel - Re: [PATCH v4 0/5] move per-vma lock into vm_area

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Message-ID: <e71408ff-b088-48e6-8b18-bb846a60cc1e@lucifer.local>
Date: Fri, 22 Nov 2024 11:56:48 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,
        Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org,
        liam.howlett@...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, dave@...olabs.net, paulmck@...nel.org,
        brauner@...nel.org, dhowells@...hat.com, hdanton@...a.com,
        hughd@...gle.com, minchan@...gle.com, jannh@...gle.com,
        souravpanda@...gle.com, pasha.tatashin@...een.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 0/5] move per-vma lock into vm_area_struct

On Thu, Nov 21, 2024 at 02:00:46AM +0000, Matthew Wilcox wrote:
> On Wed, Nov 20, 2024 at 02:10:44PM -0800, Shakeel Butt wrote:
> > If 'struct vm_area_struct' is prone to performance issues due to
> > cacheline misalignments then we should do something about the
> > __randomize_layout tag for it. I imagine we can identify the fields
> > which might be performance critical to be on same cacheline or different
> > cacheline due to false sharing then we can divide the fields into
> > different cacheline groups and fields can be __randomize_layout within
> > the group. WDYT?
>
> Pretty sure the people who think security is more important than
> performance are the only ones who randomize structs.

I agree that I don't think we need concern ourselves with users of this
setting for precisely this reason.

I wouldn't want supporting this to cause difficulty for users who do not
enable this when those who do aren't really concerned about the perf issues
as Matthew says.