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From: Rik van Riel To: Chris Li Cc: Gregory Price , Johannes Weiner , Baoquan He , Nhat Pham , Kairui Song , Michal Hocko , Roman Gushchin , Shakeel Butt , Yosry Ahmed , David Hildenbrand , Muchun Song , Kemeng Shi , Barry Song , YoungJun Park , Chengming Zhou , "Lorenzo Stoakes (Oracle)" , "Liam R. Howlett" , "Vlastimil Babka (SUSE)" , Mike Rapoport , Suren =?UTF-8?Q?Baghdasaryan=EF=BF=BC?= , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , Wenchao Hao , Jonathan Corbet , Hugh Dickins , Baolin Wang , Tejun Heo , Michal =?ISO-8859-1?Q?Koutn=FD?= , Shuah Khan , Kunwu Chan , Meta kernel team , Linux Memory Management List , Linux Kernel Mailing List , linux-doc@vger.kernel.org, "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , Andrew Morton , Kairui Song , Joshua Hahn Date: Tue, 22 Sep 2026 10:59:05 -0400 In-Reply-To: References: <785353ef79844e81a8cd97e87b00ef1f785b15e5.camel@surriel.com> <83539be885f15bb567b30264f5f62e718f4a9fd0.camel@surriel.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) MIME-Version: 1.0 X-Rspamd-Server: rspam06 X-Stat-Signature: w51o8hat8ztssr9xxhnw6tn5z37xuxw1 X-Rspam-User: X-Rspamd-Queue-Id: 0DBB38001A X-HE-Tag: 1790089260-944056 X-HE-Meta: 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 Vimo7keR 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2026-09-22 at 03:32 -1000, Chris Li wrote: > On Mon, Sep 21, 2026 at 8:53=E2=80=AFAM Rik van Riel > wrote: > >=20 > > On Mon, 2026-09-21 at 08:10 -1000, Chris Li wrote: > > > On Mon, Sep 21, 2026 at 6:40=E2=80=AFAM Rik van Riel > > > wrote: > > > >=20 > > > > On Mon, 2026-09-21 at 06:31 -1000, Chris Li wrote: > > > > >=20 > > > > > Give me some real-world examples of people hitting this kind > > > > > of > > > > > limit. > > > > > e.g. MAX(%)=C2=A0 > 100% and still have a usesable system. I > > > > > suspect > > > > > that > > > > > with 100% zswap usage, the system becomes unusable. Please > > > > > show > > > > > me a > > > > > real world case that proves me wrong. > > > > >=20 > > > >=20 > > > > Here's my desktop system right now. The amount > > > > of Zswapped is more than twice AnonPages, and > > > > the system stays perfectly usable. > > > >=20 > > > > $ grep -E '(Anon|Zswap|GPU|Swap)' /proc/meminfo > > > > SwapCached:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 252340 kB > > > > SwapTotal:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 41523604 kB > > > > SwapFree:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 9802088 kB > > > > Zswap:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = 8812236 kB > > > > Zswapped:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 24927876 kB > > > > AnonPages:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 11615760 kB > > > > AnonHugePages:=C2=A0=C2=A0 1402880 kB > > > > GPUActive:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 13112428 kB > > > > GPUReclaim:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 95980 kB > > > >=20 > > > > This is also an example where I cannot really > > > > predict how much zswap space I need, because > > > > that depends on what AI model is loaded, > > > > which drives the GPUActive number, as well > > > > as the number of browser tabs. > > > >=20 > > > > The system is perfectly responsive. > > >=20 > > > Great, that is getting somewhere. We are talking about actual > > > usage. > > > I > > > really appreciate that. > > >=20 > > > May I ask what the total amount of memory (RAM) in your system > > > is? > > >=20 > > > I am not asking zswap compare to ANA memory. I want to get the % > > > of > > > the total RAM. > > > I assume your desktop has more than 8G of RAM, right? > >=20 > > Right now it has 64GB of memory. >=20 > That is exactly my point. You are running 1/8 =3D 12.5% system ram. >=20 > My point is that, I haven't seen a case where the application is > still > usable with a reasonable SLO when 100% of RAM is zswapped out. In my numbers above, the applications have 11.6GB AnonPages, and 25GB Zswap. That is about 68% of anon memory stored in zswap. Not 8%. Out of (anon + zswap), zswap takes up 43% Can we at least agree on the observed numbers? > >=20 > > hen the amount needed to fit a workload > > does not have a positive correlation with > > the amount of system memory? >=20 > It absolutely has a positive correlation with % of the system memory > based on my experience. The % of memory swap out has a very positive > correlation with the thrashing on the application. The applications thrash much harder once zswap flows over onto disk! Out of all the swap options available, zswap is the fastest, lowest latency one. Forcing things out to disk "because too much zswap is slow" could just slow things down further. Now, there is probably some upper bound where the zswap pool itself starts to hurt performance because it's crowding the applications out of memory, but that could be quite large. --=20 All Rights Reversed.