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Tue, 26 Nov 2024 21:04:53 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:cda8:c605:6e79:8b60]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7fbcc422d0bsm8262535a12.84.2024.11.26.21.04.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Nov 2024 21:04:52 -0800 (PST) Date: Wed, 27 Nov 2024 14:04:45 +0900 From: Sergey Senozhatsky To: Barry Song <21cnbao@gmail.com> Cc: Sergey Senozhatsky , akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk, bala.seshasayee@linux.intel.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, kanchana.p.sridhar@intel.com, kasong@tencent.com, linux-block@vger.kernel.org, minchan@kernel.org, nphamcs@gmail.com, ryan.roberts@arm.com, surenb@google.com, terrelln@fb.com, usamaarif642@gmail.com, v-songbaohua@oppo.com, wajdi.k.feghali@intel.com, willy@infradead.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, zhengtangquan@oppo.com, zhouchengming@bytedance.com Subject: Re: [PATCH RFC v3 0/4] mTHP-friendly compression in zsmalloc and zram based on multi-pages Message-ID: <20241127050445.GG440697@google.com> References: <20241121222521.83458-1-21cnbao@gmail.com> <20241126050917.GC440697@google.com> <20241126105258.GE440697@google.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On (24/11/27 09:31), Barry Song wrote: > On Tue, Nov 26, 2024 at 11:53 PM Sergey Senozhatsky > wrote: > > > > On (24/11/26 14:09), Sergey Senozhatsky wrote: > > > > swap-out time(ms) 68711 49908 > > > > swap-in time(ms) 30687 20685 > > > > compression ratio 20.49% 16.9% > > > > I'm also sort of curious if you'd use zstd with pre-trained user > > dictionary [1] (e.g. based on a dump of your swap-file under most > > common workloads) would it give you desired compression ratio > > improvements (on current zram, that does single page compression). > > > > [1] https://github.com/facebook/zstd?tab=readme-ov-file#the-case-for-small-data-compression > > Not yet, but it might be worth trying. A key difference between servers and > Android phones is that phones have millions of different applications > downloaded from the Google Play Store or other sources. Maybe yes maybe not, I don't know. It could be that that 99% of users use the same 1% apps out of those millions. > In this case, would using a dictionary be a feasible approach? Apologies > if my question seems too naive. It's a good question, and there is probably only one way to answer it - through experiments, it's data dependent, so it's case-by-case. > On the other hand, the advantage of a pre-trained user dictionary > doesn't outweigh the benefits of large block compression? Can’t both > be used together? Well, so far the approach has many unmeasured unknowns and corner cases, I don't think I personally even understand all of them to begin with. Not sure if I have a way to measure and analyze, that mTHP swapout seems like a relatively new thing and it also seems that you are still fixing some of its issues/shortcomings.