The patch titled
Subject: zram: rework recompression loop
has been added to the -mm mm-unstable branch. Its filename is
zram-rework-recompression-loop.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-rework-recompression-loop.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: rework recompression loop
Date: Fri, 14 Feb 2025 13:50:21 +0900
This reworks recompression loop handling:
- set a rule that stream-put NULLs the stream pointer If the loop
returns with a non-NULL stream then it's a successfull recompression,
otherwise the stream should always be NULL.
- do not count the number of recompressions Mark object as
incompressible as soon as the algorithm with the highest priority failed
to compress that object.
- count compression errors as resource usage Even if compression has
failed, we still need to bump num_recomp_pages counter.
Link: https://lkml.kernel.org/r/20250214045208.1388854-10-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 | 53 +++++++++++---------------------
1 file changed, 19 insertions(+), 34 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zram-rework-recompression-loop
+++ a/drivers/block/zram/zram_drv.c
@@ -1929,9 +1929,8 @@ static int recompress_slot(struct zram *
unsigned int comp_len_new;
unsigned int class_index_old;
unsigned int class_index_new;
- u32 num_recomps = 0;
void *src, *dst;
- int ret;
+ int ret = 0;
handle_old = zram_get_handle(zram, index);
if (!handle_old)
@@ -1974,7 +1973,6 @@ static int recompress_slot(struct zram *
if (!zram->comps[prio])
continue;
- num_recomps++;
zstrm = zcomp_stream_get(zram->comps[prio]);
src = kmap_local_page(page);
ret = zcomp_compress(zram->comps[prio], zstrm,
@@ -1983,7 +1981,8 @@ static int recompress_slot(struct zram *
if (ret) {
zcomp_stream_put(zstrm);
- return ret;
+ zstrm = NULL;
+ break;
}
class_index_new = zs_lookup_class_index(zram->mem_pool,
@@ -1993,6 +1992,7 @@ static int recompress_slot(struct zram *
if (class_index_new >= class_index_old ||
(threshold && comp_len_new >= threshold)) {
zcomp_stream_put(zstrm);
+ zstrm = NULL;
continue;
}
@@ -2001,14 +2001,6 @@ static int recompress_slot(struct zram *
}
/*
- * We did not try to recompress, e.g. when we have only one
- * secondary algorithm and the page is already recompressed
- * using that algorithm
- */
- if (!zstrm)
- return 0;
-
- /*
* Decrement the limit (if set) on pages we can recompress, even
* when current recompression was unsuccessful or did not compress
* the page below the threshold, because we still spent resources
@@ -2017,38 +2009,31 @@ static int recompress_slot(struct zram *
if (*num_recomp_pages)
*num_recomp_pages -= 1;
- if (class_index_new >= class_index_old) {
+ /* Compression error */
+ if (ret)
+ return ret;
+
+ if (!zstrm) {
/*
* Secondary algorithms failed to re-compress the page
- * in a way that would save memory, mark the object as
- * incompressible so that we will not try to compress
- * it again.
+ * in a way that would save memory.
*
- * We need to make sure that all secondary algorithms have
- * failed, so we test if the number of recompressions matches
- * the number of active secondary algorithms.
+ * Mark the object incompressible if the max-priority
+ * algorithm couldn't re-compress it.
*/
- if (num_recomps == zram->num_active_comps - 1)
- zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+ if (prio < zram->num_active_comps)
+ return 0;
+ zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
return 0;
}
- /* Successful recompression but above threshold */
- if (threshold && comp_len_new >= threshold)
- return 0;
-
/*
- * No direct reclaim (slow path) for handle allocation and no
- * re-compression attempt (unlike in zram_write_bvec()) since
- * we already have stored that object in zsmalloc. If we cannot
- * alloc memory for recompressed object then we bail out and
- * simply keep the old (existing) object in zsmalloc.
+ * We are holding per-CPU stream mutex and entry lock so better
+ * avoid direct reclaim. Allocation error is not fatal since
+ * we still have the old object in the mem_pool.
*/
handle_new = zs_malloc(zram->mem_pool, comp_len_new,
- __GFP_KSWAPD_RECLAIM |
- __GFP_NOWARN |
- __GFP_HIGHMEM |
- __GFP_MOVABLE);
+ GFP_NOWAIT | __GFP_HIGHMEM | __GFP_MOVABLE);
if (IS_ERR_VALUE(handle_new)) {
zcomp_stream_put(zstrm);
return PTR_ERR((void *)handle_new);
_
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-two-staged-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
zsmalloc-rename-pool-lock.patch
zsmalloc-make-zspage-lock-preemptible.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
