The patch titled
Subject: mm/zswap: change dstmem size to one page
has been added to the -mm mm-unstable branch. Its filename is
mm-zswap-change-dstmem-size-to-one-page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-change-dstmem-size-to-one-page.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: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Subject: mm/zswap: change dstmem size to one page
Date: Mon, 18 Dec 2023 11:50:31 +0000
Patch series "mm/zswap: dstmem reuse optimizations and cleanups", v3.
The problem this series tries to optimize is that zswap_load() and
zswap_writeback_entry() have to malloc a temporary memory to support
!zpool_can_sleep_mapped(). We can avoid it by reusing the percpu
crypto_acomp_ctx->dstmem, which is also used by zswap_store() and
protected by the same percpu crypto_acomp_ctx->mutex.
This patch (of 6):
Change the dstmem size from 2 * PAGE_SIZE to only one page since we only
need at most one page when compress, and the "dlen" is also PAGE_SIZE in
acomp_request_set_params(). If the output size > PAGE_SIZE we don't wanna
store the output in zswap anyway.
So change it to one page, and delete the stale comment.
There is not any history about the reason why we needed 2 pages, it has
been 2 * PAGE_SIZE since the time zswap was first merged.
According to Yosry and Nhat, one potential reason is that we used to store
a zswap header containing the swap entry in the compressed page for
writeback purposes, but we don't do that anymore.
This patch works good in kernel build testing even when the input data
doesn't compress at all (i.e. dlen == PAGE_SIZE), which we can see from
the bpftrace tool:
bpftrace -e 'k:zpool_malloc {@[(uint32)arg1==4096]=count()}'
@[1]: 2
@[0]: 12011430
Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v3-0-4eac09b94ece@xxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v3-1-4eac09b94ece@xxxxxxxxxxxxx
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxx>
Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/mm/zswap.c~mm-zswap-change-dstmem-size-to-one-page
+++ a/mm/zswap.c
@@ -707,7 +707,7 @@ static int zswap_dstmem_prepare(unsigned
struct mutex *mutex;
u8 *dst;
- dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
+ dst = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu));
if (!dst)
return -ENOMEM;
@@ -1657,8 +1657,7 @@ bool zswap_store(struct folio *folio)
sg_init_table(&input, 1);
sg_set_page(&input, page, PAGE_SIZE, 0);
- /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */
- sg_init_one(&output, dst, PAGE_SIZE * 2);
+ sg_init_one(&output, dst, PAGE_SIZE);
acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
/*
* it maybe looks a little bit silly that we send an asynchronous request,
_
Patches currently in -mm which might be from zhouchengming@xxxxxxxxxxxxx are
mm-zswap-change-dstmem-size-to-one-page.patch
mm-zswap-reuse-dstmem-when-decompress.patch
mm-zswap-refactor-out-__zswap_load.patch
mm-zswap-cleanup-zswap_load.patch
mm-zswap-cleanup-zswap_writeback_entry.patch
mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store.patch
