[PATCHv2,0/7] zsmalloc: preemptible object mapping

Message

Sergey Senozhatsky Jan. 30, 2025, 4:42 a.m. UTC

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/[e-mail]

v1 -> v2:
- Tweak cmpxchg loop (Uros)
- Addressed feedback provided by Yosry

Sergey Senozhatsky (7):
  zsmalloc: factor out pool locking helpers
  zsmalloc: re-shuffle zs_pool members
  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                 | 379 ++++++++++++++++++++++++++--------
 5 files changed, 313 insertions(+), 110 deletions(-)

--
2.48.1.262.g85cc9f2d1e-goog

Comments

Sergey Senozhatsky Jan. 30, 2025, 2:21 p.m. UTC | #1

On (25/01/30 13:42), Sergey Senozhatsky wrote:
> 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

I'll combine this series and zram series [1] and send out as one patch
set.

[1] https://lore.kernel.org/linux-mm/[e-mail]