linux-kernel - [PATCH v2 0/1] remove SWAP_MAP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241002012042.2753174-1-nphamcs@gmail.com>
Date: Tue,  1 Oct 2024 18:20:41 -0700
From: Nhat Pham <nphamcs@...il.com>
To: akpm@...ux-foundation.org
Cc: hannes@...xchg.org,
	yosryahmed@...gle.com,
	hughd@...gle.com,
	shakeel.butt@...ux.dev,
	ryan.roberts@....com,
	ying.huang@...el.com,
	chrisl@...nel.org,
	david@...hat.com,
	kasong@...cent.com,
	willy@...radead.org,
	viro@...iv.linux.org.uk,
	baohua@...nel.org,
	chengming.zhou@...ux.dev,
	v-songbaohua@...o.com,
	linux-mm@...ck.org,
	kernel-team@...a.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/1] remove SWAP_MAP_SHMEM

Changelog:
v2:
	* Fix a WARN in the shmem THP swap path. Thanks Baolin, Yosry, and Barry
	for the report and the discussion on how to solve it.
	* Squash the two patches into one.
RFC v1: https://lore.kernel.org/all/20240923231142.4155415-1-nphamcs@gmail.com/

The SWAP_MAP_SHMEM state was originally introduced in the commit
aaa468653b4a ("swap_info: note SWAP_MAP_SHMEM"), to quickly determine if a
swap entry belongs to shmem during swapoff.

However, swapoff has since been rewritten drastically in the commit
b56a2d8af914 ("mm: rid swapoff of quadratic complexity"). Now
having swap count == SWAP_MAP_SHMEM value is basically the same as having
swap count == 1, and swap_shmem_alloc() behaves analogously to
swap_duplicate()

This RFC proposes the removal of this state and the associated helper to
simplify the state machine (both mentally and code-wise). We will also
have an extra state/special value that can be repurposed (for swap entries
that never gets re-duplicated).

Another motivation  is the new swap abstraction I am currently working on,
that would allow for swap/zswap decoupling, swapoff optimization, etc. The
fewer states and swap API functions there are, the simpler the conversion
will be.

Nhat Pham (1):
  swap: shmem: remove SWAP_MAP_SHMEM

 include/linux/swap.h | 16 ++++++++--------
 mm/shmem.c           |  2 +-
 mm/swapfile.c        | 41 +++++++++++++++++++++--------------------
 3 files changed, 30 insertions(+), 29 deletions(-)

base-commit: 391cad4424af8bb563e1504c5adaef0155b4abb6
-- 
2.43.5