linux-kernel - Re: [RFC PATCH 00/14] Virtual Swap Space

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Message-ID: <CAKEwX=MAeT+ag9mNq7-yfVBzgGQ7y+SN_p7DQnto01TG33EAPQ@mail.gmail.com>
Date: Tue, 8 Apr 2025 09:27:25 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Usama Arif <usamaarif642@...il.com>, linux-mm@...ck.org, akpm@...ux-foundation.org, 
	hughd@...gle.com, yosry.ahmed@...ux.dev, mhocko@...nel.org, 
	roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, muchun.song@...ux.dev, 
	len.brown@...el.com, chengming.zhou@...ux.dev, kasong@...cent.com, 
	chrisl@...nel.org, huang.ying.caritas@...il.com, ryan.roberts@....com, 
	viro@...iv.linux.org.uk, baohua@...nel.org, osalvador@...e.de, 
	lorenzo.stoakes@...cle.com, christophe.leroy@...roup.eu, pavel@...nel.org, 
	kernel-team@...a.com, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH 00/14] Virtual Swap Space

On Tue, Apr 8, 2025 at 9:25 AM Nhat Pham <nphamcs@...il.com> wrote:
>
>
> You're right. I haven't touched the swapfile swap map and the zeromap
> bitmap at all, primarily because it's non-functional change
> (optimization only). It also adds more ifdefs to the final codebase :)
>
> In the next version, I can tag on one patch to:
>
> 1. remove zeromap bitmap. This one is pretty much straightforward -
> we're not using it at all.
>
> 2. Swap map reduction. I'm like 70% sure we don't need SWAP_MAP_BAD
> state. With the vswap reverse map and the swapfile inuse counters, we
> should be able to convert the swapmap into a pure bitmap. If we can't,
> then it's 2 bits per physical swapfiles.

s/physical swapfiles/physical swap slot (3 states - unallocated,
allocated, bad slot. the latter two might be mergeable).