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Thu, 26 Sep 2024 11:30:51 +0800 Message-ID: <26f20b95-9e2f-4e8b-bf34-d13e082192d0@linux.alibaba.com> Date: Thu, 26 Sep 2024 11:30:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] remove SWAP_MAP_SHMEM To: "Huang, Ying" , Nhat Pham Cc: Yosry Ahmed , akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, shakeel.butt@linux.dev, ryan.roberts@arm.com, chrisl@kernel.org, david@redhat.com, kasong@tencent.com, willy@infradead.org, viro@zeniv.linux.org.uk, baohua@kernel.org, chengming.zhou@linux.dev, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org References: <20240923231142.4155415-1-nphamcs@gmail.com> <4d38c65d-760c-43a5-bb47-8e0235c13a51@linux.alibaba.com> <9a110f20-42ad-468b-96c6-683e162452a9@linux.alibaba.com> <85a2fd61-93d3-4cd9-95a3-e9eaef87286b@linux.alibaba.com> <87y13fqina.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Baolin Wang In-Reply-To: <87y13fqina.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C2B42180006 X-Stat-Signature: h9gsmijrhyqpgw64tnxyww6nxob56g71 X-HE-Tag: 1727321457-503152 X-HE-Meta: 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 /WqMiF+z utmuZxGvleqQBXoYgEb3Ek1OXdrL3PfXdP4iaJEbvAkQrAQnYPiE+aN64oK6556+sKC3WpT/qBebQRvXb9ttuB+nnRLkxDle8wErpvOMUa1oontDFZojRRrT+nTebkVqc5U/BI8HSZZEE74ft/q9KpE4d3CfQzFUTghjF1Xhc4kvpJk5yMg54eHOKhaGhwsxYvNG7cR+flmZy7W57rjml6wYW6hI8rpy8RHEPrPSk/o8CYF04qZ0VaYl6eaHOGW3ogwEKx11pmpgnXQm+R0gxOrq+KG03u1TZ8Ph8tiR7uftQlQm49w7xxkETtjMw2QbNeCjXECz1r32ZOTuQcD0FsMs2UkXn4UiaUfeVNLwkAIDYZaPul5O0eP9ixw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 2024/9/26 09:59, Huang, Ying wrote: > Nhat Pham writes: > >> On Tue, Sep 24, 2024 at 6:53 PM Baolin Wang >> wrote: >>> >>> >>> One benefit I can mention is that removing 'SWAP_MAP_SHMEM' can help to >>> batch free shmem swap entries in __swap_entries_free(), similar to the >>> commit bea67dcc5eea ("mm: attempt to batch free swap entries for >>> zap_pte_range()") did, which can improve the performance of shmem mTHP >>> munmap() function based on my testing. >> >> Yeah, the problem with having an extraneous state is you have to >> constantly check for it in code, and/or keep it in mind when you >> develop things. I've been constantly having to check for this state >> when I develop code around this area, and it gets old fast. >> >> If we can use it to optimize something, I can understand keeping it. >> But it just seems like dead code to me :) >> >> My preference is to do this as simply as possible - add another case >> (usage == 1, nr > 1, and we need to add swap continuations) in the >> check in __swap_duplicate()'s first loop, and just WARN right there. >> >> That case CANNOT happen UNLESS we introduce a bug, or have a new use >> case. When we actually have a use case, we can always introduce >> handling/fallback logic for that case. >> >> Barry, Yosry, Baolin, Ying, how do you feel about this? > > Sounds good to me to just WARN now. We can always improve when it's > necessary. +1. Agreed.