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Wed, 17 Jan 2024 16:49:38 -0800 (PST) MIME-Version: 1.0 References: <20240117-b4-zswap-lock-optimize-v1-0-23f6effe5775@bytedance.com> In-Reply-To: From: Nhat Pham Date: Wed, 17 Jan 2024 16:49:27 -0800 Message-ID: Subject: Re: [PATCH 0/2] mm/zswap: optimize the scalability of zswap rb-tree To: Chris Li Cc: Yosry Ahmed , Chengming Zhou , Andrew Morton , linux-kernel@vger.kernel.org, Johannes Weiner , linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 50DCF180010 X-Stat-Signature: 5gddura4py98ub3ziyzo9zqcwcffccid X-Rspam-User: X-HE-Tag: 1705538979-515869 X-HE-Meta: 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 liSRAAYf nt/ecN8K3TLFUbkfFLK0HmZAyljVew2rM1LvAL+0ElrOGeaJc63J99vtT6fpz0DPZj1SowEgzzC3CbqzYOhih8WGzIlJfHKZw5a6yc0RE0KE7huM7VV2n3ZNv0YnPrgaGs/bRoxQMoTk4pWKkMTHrn1D4YTlijz6kp/RD5iIy9yKsX/+a0RZDR43XCVxgmtycc5t+hMJG73sAVRzRxI762Aetwyl9a13fp23B6TISoQThHzMjFEl1zRO/MJTaVCEFzr8Ymv4/ug9PkNZWCmcpOQIJUB9uoJiauGPfrzOTy/RCnCj9yvDAesc8Kcud0pEjnmee8PWhNSGVhwvThZzJiNMEDVTN12UodLTEzurgTYFTwRsjtgg7p+3yId309WelRqhCDA603eT2I+HwUbxIsE4y/YdOofcTcLeVZEtwTl1gkKTmbESa9JMxAA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.174223, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jan 17, 2024 at 4:18=E2=80=AFPM Chris Li wrote: > > Hi Yosry, > > On Wed, Jan 17, 2024 at 3:48=E2=80=AFPM Yosry Ahmed wrote: > > > > > Currently the xarray patch should have everything it takes to use RCU > > > read lock. However taking out the tree spinlock is more work than > > > previously. If we are going to remove the tree spinlock, I think we > > > should revert back to doing a zswap tree lookup and return the zswap > > > entry with reference increased. The tree mapping can still decouple > > > from the zswap entry reference count drop to zero. Anyway, my V1 of > > > the xarray patch will not include removing the tree spinlock. > > > > Interesting. What do you mean by removing the tree spinlock? My > > assumption was that the xarray reduces lock contention because we do > > not need a lock to do lookups, but we still need the lock otherwise. > > Did you have something in mind to completely remove the tree lock? > > In my current xarray series, it adds the xarray alongside the rb tree. Hmmm why? Is there a reason to keep the rb tree around?