linux-kernel - [PATCHv1 0/6] zsmalloc: preemptible object mapping

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Message-ID: <20250129064853.2210753-1-senozhatsky@chromium.org>
Date: Wed, 29 Jan 2025 15:43:46 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Yosry Ahmed <yosry.ahmed@...ux.dev>,
	Nhat Pham <nphamcs@...il.com>
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCHv1 0/6] zsmalloc: preemptible object mapping

This is Part II of the series [1] that makes zram read() and write()
preemptible.  This part focuses only zsmalloc because zsmalloc imposes
atomicity restrictions on its users.  One notable example is object
mapping API, which returns with:
a) local CPU lock held
b) zspage rwlock held

First, zsmalloc is converted to use sleepable RW-"lock" (it's atomic_t
in fact) for zspage migration protection.  Second, a new handle mapping
is introduced which doesn't use per-CPU buffers (and hence no local CPU
lock), does fewer memcpy() calls, but requires users to provide a
pointer to temp buffer for object copy-in (when needed).  Third, zram is
converted to the new zsmalloc mapping API and thus zram read() becomes
preemptible.

[1] https://lore.kernel.org/linux-mm/20250127072932.1289973-1-senozhatsky@chromium.org

RFC -> v1:
- Only zspage->lock (leaf-lock for zs_map_object()) is converted
  to a preemptible lock.  The rest of the zspool locks remain the
  same (Yosry hated with passion the fact that in RFC series all
  zspool looks would become preemptible).
- New zs object mapping API (Yosry hated RFC API with passion).
  We know have obj_read_begin()/obj_read_end() and obj_write().
- obj_write() saves extra memcpy() calls for objects that span two
  physical pages.
- Dropped zram deferred slot-free-notification handling (I hated
  it with passion)

Sergey Senozhatsky (6):
  zsmalloc: factor out pool locking helpers
  zsmalloc: factor out size-class locking helpers
  zsmalloc: make zspage lock preemptible
  zsmalloc: introduce new object mapping API
  zram: switch to new zsmalloc object mapping API
  zram: add might_sleep to zcomp API

 drivers/block/zram/zcomp.c    |   6 +-
 drivers/block/zram/zcomp.h    |   2 +
 drivers/block/zram/zram_drv.c |  28 +--
 include/linux/zsmalloc.h      |   8 +
 mm/zsmalloc.c                 | 372 ++++++++++++++++++++++++++--------
 5 files changed, 311 insertions(+), 105 deletions(-)

-- 
2.48.1.262.g85cc9f2d1e-goog