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Tue, 08 Sep 2026 11:30:15 -0700 (PDT) Date: Tue, 8 Sep 2026 14:30:11 -0400 From: Johannes Weiner To: Kairui Song Cc: Nhat Pham , Chris Li , Michal Hocko , Roman Gushchin , Shakeel Butt , Yosry Ahmed , David Hildenbrand , Muchun Song , Kemeng Shi , Baoquan He , Barry Song , YoungJun Park , Chengming Zhou , "Lorenzo Stoakes (Oracle)" , "Liam R. Howlett" , "Vlastimil Babka (SUSE)" , Mike Rapoport , Suren =?utf-8?B?QmFnaGRhc2FyeWFu77+8?= , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , Rik van Riel , Gregory Price , 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 , Joshua Hahn Subject: Re: Path forward for Virtualized Swap? Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 99A7EA000A X-Stat-Signature: 374tqxh71ngp8rpy6t6ijdzhyiz9ogb1 X-Rspam-User: X-HE-Tag: 1788892217-559258 X-HE-Meta: U2FsdGVkX1/WjeWCzmMTBxHc7jbe/VTW640MuvZMZnx5GmcwJkVAgjddoGxbGEuUzog8LDCm1yLA495qj3Um5+gke93c0jlBTnwpiJYsIJiAmYzu/8O8zqeAsQF7zmtvG6zmkxUo1Tek56PgJbUDmjgBPOSlRCnFhDu2qWjh72CxaVKAG8DceIugmSklg2d5uU40p7Y042ymaxt5LUL9pglDxBRmr3LEYS/G433JHwaSKNUfQGra0ehInGLDeEWgYtv7ufygVJPW7P8lgLH+DU90w4662a6Vi9NSTIzDdmSe7bp63vCnwauEf09T2BfvfmfhkYF51vDoHBRigfmMH559Oi9bnOdF0BEbbpTgsxksHvcVpiS5cyKE9ptHexQjbpEeSrw3MHZMoBxdweeOE8vB4wN7Z+ogBrkPF+Okpvyj6/kaODHI1/LQ5FP+rIe+4b880l3uvLtUSK3MwjOxkqI7y0j+nJmvCzSPr8vwa1foPFR41jFzJ8BOAqMDLNoqlkU9vAn/UH9VOpvSpCnvgU0N0N6+QfKv4Gar9PEc5icDjGv0mWNXGXlToj8Ssbv79xN7ZuK3nRkoy0YDvEzrlYtE9GTy2Cwar/akf2xQLXQZs15FcdaVCyvTc9QhT/0agPdvIpN8TtkvE2KVVT3SxAL/HgcMSb3n7l0udjqB4DkiCEACL4eN9qQJI679KJ31ekZ7VZzvfDxgPq8UJgReWyQ7KH9SspcEMpH3TjDawZNdgh7VtqYHv2KmvhGL7gVSVrVW4JdEbGzv0iYs4KoBBFhuTRfnF1g8q1p8Xst7ddjSjjJxtIYWEAEiHFnNONsUSBag1K6koILqP29PtdGG2vWe4yi9v84fLS0hxaLFM21wq1OypnxnMZD7LQZVjMtsZuDByYpbuA4jb4bgCfAj3aMAAdLLTRPz64Ff9zvMs31fkRm12ylvUZrohML2AaS4guOe4Vwpyy5C+sOYPBR 5gCUt56K 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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 Mon, Sep 07, 2026 at 01:51:31PM +0800, Kairui Song wrote: > Where I've ended up is that unbounded growth is a real concern. On a > host with no memcg limit (root cgroup, and most desktop and embedded > setups), an unlimited pool means usage can keep growing, with no > admin visible ceiling at all. I'm not attached to xswap's percent of RAM > knob specifically, but I do think some kind of bound makes sense. Swap space is just process virtual address space, no? Swap entries already have one or more page table entries pointing to them, which in turn are managed by trees of vm_area_structs. That means rlimits apply, overcommit protection applies, and OOM killer attribution works as well (oom_badness()). Shmem has its own defaults and limit interface on address space. I'm not quite seeing how the swap space needs an additional limit. How could users break things in unique new ways without it? It would be good to spell out that vector before discussing numbers :)