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Date:   Tue, 9 Jun 2020 14:03:28 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Michel Lespinasse <walken@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Liam Howlett <Liam.Howlett@oracle.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        David Rientjes <rientjes@google.com>,
        Hugh Dickins <hughd@google.com>, Ying Han <yinghan@google.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v6 00/12] Add a new mmap locking API wrapping mmap_sem
 calls
Message-ID: <20200609120328.GB22623@dhcp22.suse.cz>
References: <20200520052908.204642-1-walken@google.com>
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Hi,

On Tue 19-05-20 22:28:56, Michel Lespinasse wrote:
> Reposting this patch series on top of v5.7-rc6. I think this is ready
> for inclusion into the -mm tree; however there were some minor points
> of feedback to address and also it was easier to regenerate a full
> version after the v5.5 (only updating patches 09/10 and 10/10) caused
> some confusion.
> 
> 
> This patch series adds a new mmap locking API replacing the existing
> mmap_sem lock and unlocks. Initially the API is just implemente in terms
> of inlined rwsem calls, so it doesn't provide any new functionality.
> 
> There are two justifications for the new API:
> 
> - At first, it provides an easy hooking point to instrument mmap_sem
>   locking latencies independently of any other rwsems.
> 
> - In the future, it may be a starting point for replacing the rwsem
>   implementation with a different one, such as range locks. This is
>   something that is being explored, even though there is no wide concensus
>   about this possible direction yet.
>   (see https://patchwork.kernel.org/cover/11401483/)

Sorry that I am jumping late to the game.

Even though I hoped that the new API would somehow start using a
concept of address ranges, because I believe this is a fundamental lock
granularity for this mmap_sem, this is definitely a step in the right
direction. Getting rid of all direct usage of mmap_sem is an
improvement in itself.

Feel free to add
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!
-- 
Michal Hocko
SUSE Labs