linux-kernel - Re: [PATCH v2 5/5] docs/mm: document latest changes to vm

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Message-ID: <322783ad-ddb1-4444-8c81-4c3d368fac66@lucifer.local>
Date: Wed, 13 Nov 2024 14:46:44 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, willy@...radead.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, shakeel.butt@...ux.dev, souravpanda@...gle.com,
        pasha.tatashin@...een.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] docs/mm: document latest changes to vm_lock

On Tue, Nov 12, 2024 at 11:51:47AM -0800, Suren Baghdasaryan wrote:
> On Tue, Nov 12, 2024 at 11:47 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > Change the documentation to reflect that vm_lock is integrated into vma.
> > Document newly introduced vma_start_read_locked{_nested} functions.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Thanks!

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

>
> Sorry, forgot to CC Mr. Corbet and linux-doc@...r. Added now.
>
> > ---
> >  Documentation/mm/process_addrs.rst | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/mm/process_addrs.rst b/Documentation/mm/process_addrs.rst
> > index ed74685ffbf2..c8935509173e 100644
> > --- a/Documentation/mm/process_addrs.rst
> > +++ b/Documentation/mm/process_addrs.rst
> > @@ -675,7 +675,11 @@ RCU critical section, then attempts to VMA lock it via
> >  :c:func:`!vma_start_read`, before releasing the RCU lock via
> >  :c:func:`!rcu_read_unlock`.
> >
> > -VMA read locks hold the read lock on the :c:member:`!vma->vm_lock` semaphore for
> > +In cases when the user already holds mmap read lock, :c:func:`!vma_start_read_locked`
> > +and :c:func:`!vma_start_read_locked_nested` can be used. These functions always
> > +succeed in acquiring VMA read lock.
> > +
> > +VMA read locks hold the read lock on the :c:member:`!vma.vm_lock` semaphore for
> >  their duration and the caller of :c:func:`!lock_vma_under_rcu` must release it
> >  via :c:func:`!vma_end_read`.
> >
> > @@ -739,7 +743,7 @@ keep VMAs locked across entirely separate write operations. It also maintains
> >  correct lock ordering.
> >
> >  Each time a VMA read lock is acquired, we acquire a read lock on the
> > -:c:member:`!vma->vm_lock` read/write semaphore and hold it, while checking that
> > +:c:member:`!vma.vm_lock` read/write semaphore and hold it, while checking that
> >  the sequence count of the VMA does not match that of the mm.
> >
> >  If it does, the read lock fails. If it does not, we hold the lock, excluding
> > @@ -749,7 +753,7 @@ Importantly, maple tree operations performed in :c:func:`!lock_vma_under_rcu`
> >  are also RCU safe, so the whole read lock operation is guaranteed to function
> >  correctly.
> >
> > -On the write side, we acquire a write lock on the :c:member:`!vma->vm_lock`
> > +On the write side, we acquire a write lock on the :c:member:`!vma.vm_lock`
> >  read/write semaphore, before setting the VMA's sequence number under this lock,
> >  also simultaneously holding the mmap write lock.
> >
> > --
> > 2.47.0.277.g8800431eea-goog
> >