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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: Wed, 23 Sep 2026 10:21:10 -0400 In-Reply-To: References: <785353ef79844e81a8cd97e87b00ef1f785b15e5.camel@surriel.com> <83539be885f15bb567b30264f5f62e718f4a9fd0.camel@surriel.com> <02616d611c9e862afc6c8c3118b6be096756b3bb.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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A3A7F80008 X-Stat-Signature: tf1xuuof6uifa4htxqmp8uwup3n4wjju X-HE-Tag: 1790173345-307189 X-HE-Meta: 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 LHkbJFve V0ExxeFkSInKjMcAjEqF4qK3fgxgizu5pHjhBVg3mZoO46xjayTCjcNha+1rwNVgENDIraIvF5yMsU7Fa43nLKsUW33q7YFjRJCRjaJhoo8CBquwXlTptekj2z8/Ax+Da+CiV08oUmqHybbyWIDfAkfUstt7tOBzGE0K1EK66kofox4jtkpGaDv2AsmH5of5NRIzv4EKiei1JpP7kdlZm8L7hsB5uO/jVFlT/fx9jOJjzb5vct/H24C0bkPmCKgzgpmWJ33MN4TR+JtaOVsiK01Feoc/QiPn6Pj83fDil3dRjDdZdv1Zlst50AjkBCsKj88EDNZZyIpAK2jaJ5hdA2ytWKLPnMyrqKkKlPm/6xQMpP5SHjRjidYu/aMqDnDcz5tyCWOclPr8dLq+Pb7q14yUO+MnBEjg3Vgpv03RbPFROhX9MWY8qCrAx4KhqVWMCcXjIVyow0RCdk80= 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 21:00 -1000, Chris Li wrote: > On Tue, Sep 22, 2026 at 5:49=E2=80=AFAM Rik van Riel > wrote: >=20 > >=20 > > However, your configuration values are not a good > > default for my setup. > >=20 > > I believe we need to set the default to something > > that accommodates a diverse range of desktop and > > mobile users. >=20 > Act. That is why I am asking for the maximum percentage that > represents the upper bound for an actual usage case. >=20 I think the workload that can use the most zswap is probably a build system that places its temporary files in tmpfs, in order to cut down on SSD wear. Those files are just sitting there most of the time, and are not part of the working set. I suspect for such a workload we could get away with maybe 30-40% of memory taken by the zswap pool, which with a 4:1 compression ratio would correspond to 120-160% of memory zswapped. At a more pessimistic 3:1 compression ratio, which seems to be fairly typical, it would be 90-120%. > >=20 > > Most of those users do not know what they will need, > > but they will know to close a few browser tabs when > > things get slow. >=20 > They don't need to know. Such a bound exists naturally. We just want > a > safe margin. You say such a boundary doesn't exist. I say that > boundary exists; that is the main contention. >=20 The current default in Linux is to allow the zswap pool to take up to 20% of memory. That results in 60-80% of memory swapped out to zswap at most, at typical compression ratios=C2=A0 of between 3:1 to 4:1. I suspect a few workloads would benefit from having a larger zswap pool. > I agree; I wouldn't want to configure each machine differently all > the > time. In my mind, swapping out that much system RAM to zswap already > results in a very unusable system. If you haven't try that, I suggest > you try it before suggesting a number > 100%. At 100%, it is not a > usable system, so we don't need to make a default for that. > Defaulting > to 8PB or 8TB is way too much. But we don't have a default size. Zswap starts at size 0. The memory is only allocated when it is needed. The vswap data structures are the same. They get allocated when they are needed, and freed when they are no longer needed. It isn't like we need to pre-allocate anything. --=20 All Rights Reversed.