The patch titled
Subject: zram: remove second stage of handle allocation
has been added to the -mm mm-unstable branch. Its filename is
zram-remove-second-stage-of-handle-allocation.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-remove-second-stage-of-handle-allocation.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@xxxxxxxxxxxx>
Subject: zram: remove second stage of handle allocation
Date: Mon, 3 Mar 2025 11:03:14 +0900
Previously zram write() was atomic which required us to pass
__GFP_KSWAPD_RECLAIM to zsmalloc handle allocation on a fast path and
attempt a slow path allocation (with recompression) if the fast path
failed.
Since we are not in atomic context anymore we can permit direct reclaim
during handle allocation, and hence can have a single allocation path.
There is no slow path anymore so we don't unlock per-CPU stream (and don't
lose compressed data) which means that there is no need to do
recompression now (which should reduce CPU and battery usage).
Link: https://lkml.kernel.org/r/20250303022425.285971-6-senozhatsky@xxxxxxxxxxxx
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Kairui Song <ryncsn@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Yosry Ahmed <yosry.ahmed@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 39 +++++---------------------------
1 file changed, 7 insertions(+), 32 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zram-remove-second-stage-of-handle-allocation
+++ a/drivers/block/zram/zram_drv.c
@@ -1723,11 +1723,11 @@ static int write_incompressible_page(str
static int zram_write_page(struct zram *zram, struct page *page, u32 index)
{
int ret = 0;
- unsigned long handle = -ENOMEM;
- unsigned int comp_len = 0;
+ unsigned long handle;
+ unsigned int comp_len;
void *dst, *mem;
struct zcomp_strm *zstrm;
- unsigned long element = 0;
+ unsigned long element;
bool same_filled;
/* First, free memory allocated to this slot (if any) */
@@ -1741,7 +1741,6 @@ static int zram_write_page(struct zram *
if (same_filled)
return write_same_filled_page(zram, element, index);
-compress_again:
zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
mem = kmap_local_page(page);
ret = zcomp_compress(zram->comps[ZRAM_PRIMARY_COMP], zstrm,
@@ -1751,7 +1750,6 @@ compress_again:
if (unlikely(ret)) {
zcomp_stream_put(zstrm);
pr_err("Compression failed! err=%d\n", ret);
- zs_free(zram->mem_pool, handle);
return ret;
}
@@ -1760,35 +1758,12 @@ compress_again:
return write_incompressible_page(zram, page, index);
}
- /*
- * handle allocation has 2 paths:
- * a) fast path is executed with preemption disabled (for
- * per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
- * since we can't sleep;
- * b) slow path enables preemption and attempts to allocate
- * the page with __GFP_DIRECT_RECLAIM bit set. we have to
- * put per-cpu compression stream and, thus, to re-do
- * the compression once handle is allocated.
- *
- * if we have a 'non-null' handle here then we are coming
- * from the slow path and handle has already been allocated.
- */
- if (IS_ERR_VALUE(handle))
- handle = zs_malloc(zram->mem_pool, comp_len,
- __GFP_KSWAPD_RECLAIM |
- __GFP_NOWARN |
- __GFP_HIGHMEM |
- __GFP_MOVABLE);
+ handle = zs_malloc(zram->mem_pool, comp_len,
+ GFP_NOIO | __GFP_NOWARN |
+ __GFP_HIGHMEM | __GFP_MOVABLE);
if (IS_ERR_VALUE(handle)) {
zcomp_stream_put(zstrm);
- atomic64_inc(&zram->stats.writestall);
- handle = zs_malloc(zram->mem_pool, comp_len,
- GFP_NOIO | __GFP_HIGHMEM |
- __GFP_MOVABLE);
- if (IS_ERR_VALUE(handle))
- return PTR_ERR((void *)handle);
-
- goto compress_again;
+ return PTR_ERR((void *)handle);
}
if (!zram_can_store_page(zram)) {
_
Patches currently in -mm which might be from senozhatsky@xxxxxxxxxxxx are
zram-sleepable-entry-locking.patch
zram-permit-preemption-with-active-compression-stream.patch
zram-remove-unused-crypto-include.patch
zram-remove-max_comp_streams-device-attr.patch
zram-remove-second-stage-of-handle-allocation.patch
zram-add-gfp_nowarn-to-incompressible-zsmalloc-handle-allocation.patch
zram-remove-writestall-zram_stats-member.patch
zram-limit-max-recompress-prio-to-num_active_comps.patch
zram-filter-out-recomp-targets-based-on-priority.patch
zram-rework-recompression-loop.patch
zram-move-post-processing-target-allocation.patch
zsmalloc-rename-pool-lock.patch
zsmalloc-sleepable-zspage-reader-lock.patch
zsmalloc-introduce-new-object-mapping-api.patch
zram-switch-to-new-zsmalloc-object-mapping-api.patch
zram-permit-reclaim-in-zstd-custom-allocator.patch
zram-do-not-leak-page-on-recompress_store-error-path.patch
zram-do-not-leak-page-on-writeback_store-error-path.patch
zram-add-might_sleep-to-zcomp-api.patch
