+ zswap-do-not-allocate-from-atomic-pool.patch added to mm-unstable branch

+ zswap-do-not-allocate-from-atomic-pool.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: zswap: do not allocate from atomic pool
has been added to the -mm mm-unstable branch.  Its filename is
     zswap-do-not-allocate-from-atomic-pool.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zswap-do-not-allocate-from-atomic-pool.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zswap: do not allocate from atomic pool
Date: Tue, 22 Nov 2022 12:30:22 +0900

zswap_frontswap_load() should be called from preemptible context (we even
call mutex_lock() there) and it does not look like we need to do
GFP_ATOMIC allocaion for temp buffer.  The same applies to
zswap_writeback_entry().

Use GFP_KERNEL for temporary buffer allocation in both cases.

Link: https://lkml.kernel.org/r/Y3xCTr6ikbtcUr/y@google.com
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zpool.c |    7 +++++++
 mm/zswap.c |    4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

--- a/mm/zpool.c~zswap-do-not-allocate-from-atomic-pool
+++ a/mm/zpool.c
@@ -387,6 +387,13 @@ bool zpool_evictable(struct zpool *zpool
  * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
  * @zpool:	The zpool to test
  *
+ * Some allocators enter non-preemptible context in ->map() callback (e.g.
+ * disable pagefaults) and exit that context in ->unmap(), which limits what
+ * we can do with the mapped object. For instance, we cannot wait for
+ * asynchronous crypto API to decompress such an object or take mutexes
+ * since those will call into the scheduler. This function tells us whether
+ * we use such an allocator.
+ *
  * Returns: true if zpool can sleep; false otherwise.
  */
 bool zpool_can_sleep_mapped(struct zpool *zpool)
--- a/mm/zswap.c~zswap-do-not-allocate-from-atomic-pool
+++ a/mm/zswap.c
@@ -958,7 +958,7 @@ static int zswap_writeback_entry(struct
 	};
 
 	if (!zpool_can_sleep_mapped(pool)) {
-		tmp = kmalloc(PAGE_SIZE, GFP_ATOMIC);
+		tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
 		if (!tmp)
 			return -ENOMEM;
 	}
@@ -1311,7 +1311,7 @@ static int zswap_frontswap_load(unsigned
 	}
 
 	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
-		tmp = kmalloc(entry->length, GFP_ATOMIC);
+		tmp = kmalloc(entry->length, GFP_KERNEL);
 		if (!tmp) {
 			ret = -ENOMEM;
 			goto freeentry;
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

zram-preparation-for-multi-zcomp-support.patch
zram-add-recompression-algorithm-sysfs-knob.patch
zram-factor-out-wb-and-non-wb-zram-read-functions.patch
zram-introduce-recompress-sysfs-knob.patch
zram-introduce-recompress-sysfs-knob-fix.patch
zram-add-recompress-flag-to-read_block_state.patch
zram-clarify-writeback_store-comment.patch
zram-use-is_err_value-to-check-for-zs_malloc-errors.patch
zram-remove-redundant-checks-from-zram_recompress.patch
zram-add-algo-parameter-support-to-zram_recompress.patch
documentation-add-zram-recompression-documentation.patch
zram-add-incompressible-writeback.patch
zram-add-incompressible-flag-to-read_block_state.patch
docs-abi-zram-document-zram-recompress-sysfs-knobs.patch
zram-remove-unused-stats-fields.patch
zswap-do-not-allocate-from-atomic-pool.patch