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Thu, 12 Feb 2026 09:57:51 -0800 (PST) MIME-Version: 1.0 References: <20260126065242.1221862-1-youngjun.park@lge.com> In-Reply-To: <20260126065242.1221862-1-youngjun.park@lge.com> From: Nhat Pham Date: Thu, 12 Feb 2026 09:57:40 -0800 X-Gm-Features: AZwV_Qj8afqc0fwywStVAnuIAl3u22UxJ3GgjvwlQjimQSLzvC_WWxVKFk3xE_E Message-ID: Subject: Re: [RFC PATCH v2 0/5] mm/swap, memcg: Introduce swap tiers for cgroup based swap control To: Youngjun Park Cc: Andrew Morton , linux-mm@kvack.org, Chris Li , Kairui Song , Kemeng Shi , Baoquan He , Barry Song , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , gunho.lee@lge.com, taejoon.song@lge.com, austin.kim@lge.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7040F20005 X-Stat-Signature: jtxf3tghxt6i96qdzjtgdh59j1x1ewm8 X-Rspam-User: X-HE-Tag: 1770919073-125318 X-HE-Meta: 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 hIK79yyU 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 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 Sun, Jan 25, 2026 at 10:53=E2=80=AFPM Youngjun Park wrote: > > This is the second version of the RFC for the "Swap Tiers" concept. > Link to v1: https://lore.kernel.org/linux-mm/20251109124947.1101520-1-you= ngjun.park@lge.com/ > > This version incorporates feedback received during LPC 2025 and addresses > comments from the previous review. We have also included experimental > results based on usage scenarios intended for our internal platforms. > > Motivation & Concept recap > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D > Current Linux swap allocation is global, limiting the ability to assign > faster devices to specific cgroups. Our initial attempt at per-cgroup > priorities proved over-engineered and caused LRU inversion. > > Following Chris Li's suggestion, we pivoted to "Swap Tiers." A tier is > simply a user-named group of swap devices sharing the same priority range= . > This abstraction facilitates swap device selection based on speed, allowi= ng > users to configure specific tiers for cgroups. > > For more details, please refer to the LPC 2025 presentation > https://lpc.events/event/19/contributions/2141/attachments/1857/3998/LPC2= 025Finalss.pdf > or v1 patch. > > Changes in v2 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > 1. Respect cgroup hierarchy principle (LPC 2025 feedback) > - The logic now strictly follows standard cgroup hierarchy principles. > > Previous: Children could select any tier using "+" regardless of the > parent's configuration. "+" tier is referenced. (could not be silently di= sappeared) > > Current: The explicit selection ("+") concept is removed. By > default, all tiers are selected. Users now use "-" to exclude specific > tiers. Excluded tier could disappeared silently. > A child cgroup is always a subset of its parent. Even if a child > re-enables a tier with "+" that was excluded by the parent, the effective > tier list is limited to the parent's allowed subset. This comment seems a bit clunky to me. The "+" is removed, as noted above, but then why are we saying "even if a child re-enables a tier with "+"" here? Am I missing something? > > Example: > Global Tiers: SSD, HDD, NET > Parent: SSD, NET (HDD excluded) > Child: HDD, NET (SSD excluded) > -> Effective Child Tier: NET (Intersection of Parent and Child) But otherwise, I assume you mean to restrict child's allowed swap tiers to be a subset of children and its ancestors? That seems more straightforward to me than the last system :)