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Sun, 1 May 2022 13:38:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1651437489; bh=tCCVnocf3mgYD9VNhEdRpcvRc6dfJeJKHpburFD1alE=; h=Date:From:To:Cc:Subject:Content-Type; b=UPvpLYfbJ2bOSCBFt/X2+o0JSM2pH3gHgWHgBQvOg/Rj9JvpyqL23UFh4uX4SLx/t QbPfYMKb6dmlZKoHpAmbrtfu3KUdlHWgTdHiaZoWWwJXS5Wj4ETxlthiPlqxfwAghj oFT9Sk4WbEYhYSy2fg8Jd7algK7jOYKA0BNtlP0qmeYWOx2a81azHmRb3KC2alPzso MjM70/+F/IHygPnXNBp4Dpf81weDDnvqRzQFlZ9s9aI32mg91UBQi5AEXe1EwAryyH JG9P2Yjq4Vr9zAYronRvGK74pNwCcs5/SVIvLCY8GrTp//i2IJTuFsCQtQiVNtUoiF Nmh/nsC8khXIw== Date: Sun, 1 May 2022 13:26:34 -0700 From: Davidlohr Bueso To: Matthew Wilcox Cc: Andrew Morton , Liam Howlett , "maple-tree@lists.infradead.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Yu Zhao Subject: Re: [PATCH v8 00/70] Introducing the Maple Tree Message-ID: <20220501202532.y6zmznzshbe33nwx@offworld> Mail-Followup-To: Matthew Wilcox , Andrew Morton , Liam Howlett , "maple-tree@lists.infradead.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Yu Zhao References: <20220426150616.3937571-1-Liam.Howlett@oracle.com> <20220426130857.09f40743b42b5f0bf4f19a59@linux-foundation.org> <20220427140832.mpvnnkkhrbupk46i@revolver> <20220427103331.9876ad87626af0f50e9ced0d@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20220408 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 27 Apr 2022, Matthew Wilcox wrote: >On Wed, Apr 27, 2022 at 10:33:31AM -0700, Andrew Morton wrote: >> On Wed, 27 Apr 2022 14:08:39 +0000 Liam Howlett wrote: >> > The benchmarks are around the same as they have always been. >> >> So it's presently a wash. >> >> That makes "the plan" (below) really critical, otherwise there seems >> little point in merging this code at this time? >> >> Please send me many very soothing words about how confident we should >> be that the plan will be implemented and that it shall be good? > >Yes, performance-wise it's a wash. However, Davidlohr was very >impressed that it was a wash because we're actually getting rid of three >data structures here; the linked list, the rbtree and the vmacache. >His opinion was that we should push the maple tree in now, in advance >of the future RCU uses. Yes I like the maple tree, and at this stage I don't think we can ask for more from this series wrt the MM - albeit there seems to still be some folks reporting breakage. Fundamentally I see Liam's work to (re)move complexity out of the MM (not to say that the actual maple tree is not complex) by consolidating the three complimentary data structures very much worth it considering performance does not take a hit. This was very much a turn off with the range locking approach, which worst case scenario incurred in prohibitive overhead. Also as Liam and Matthew have mentioned, RCU opens up a lot of nice performance opportunities, and in addition academia[1] has shown outstanding scalability of address spaces with the foundation of replacing the locked rbtree with RCU aware trees. [1] https://pdos.csail.mit.edu/papers/rcuvm:asplos12.pdf Thanks, Davidlohr