The patch titled
Subject: zswap: update docs for runtime-changeable attributes
has been added to the -mm tree. Its filename is
zswap-update-docs-for-runtime-changeable-attributes-v2.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zswap-update-docs-for-runtime-changeable-attributes-v2.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zswap-update-docs-for-runtime-changeable-attributes-v2.patch
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From: Dan Streetman <ddstreet@xxxxxxxx>
Subject: zswap: update docs for runtime-changeable attributes
changes since v1:
update doc on working of zbud per Vlastimil Babka's suggestion
add explanation of how old pages are handled when changing zpool/compressor
Signed-off-by: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Seth Jennings <sjennings@xxxxxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/vm/zswap.txt | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff -puN Documentation/vm/zswap.txt~zswap-update-docs-for-runtime-changeable-attributes-v2 Documentation/vm/zswap.txt
--- a/Documentation/vm/zswap.txt~zswap-update-docs-for-runtime-changeable-attributes-v2
+++ a/Documentation/vm/zswap.txt
@@ -61,12 +61,11 @@ sysfs "zpool" attribute, e.g.
echo zbud > /sys/module/zswap/parameters/zpool
The zbud type zpool allocates exactly 1 page to store 2 compressed pages, which
-means the compression ratio will always be exactly 2:1 (not including half-full
-zbud pages), and any page that compresses to more than 1/2 page in size will be
-rejected (and written to the swap disk). The zsmalloc type zpool has a more
-complex compressed page storage method, and it can achieve greater storage
-densities. However, zsmalloc does not implement compressed page eviction, so
-once zswap fills it cannot evict the oldest page, it can only reject new pages.
+means the compression ratio will always be 2:1 or worse (because of half-full
+zbud pages). The zsmalloc type zpool has a more complex compressed page
+storage method, and it can achieve greater storage densities. However,
+zsmalloc does not implement compressed page eviction, so once zswap fills it
+cannot evict the oldest page, it can only reject new pages.
When a swap page is passed from frontswap to zswap, zswap maintains a mapping
of the swap entry, a combination of the swap type and swap offset, to the zpool
@@ -93,5 +92,11 @@ at runtime using the sysfs "compressor"
echo lzo > /sys/module/zswap/parameters/compressor
+When the zpool and/or compressor parameter is changed at runtime, any existing
+compressed pages are not modified; they are left in their own zpool. When a
+request is made for a page in an old zpool, it is uncompressed using its
+original compressor. Once all pages are removed from an old zpool, the zpool
+and its compressor are freed.
+
A debugfs interface is provided for various statistic about pool size, number
of pages stored, and various counters for the reasons pages are rejected.
_
Patches currently in -mm which might be from ddstreet@xxxxxxxx are
zpool-add-zpool_has_pool.patch
zpool-add-zpool_has_pool-fix.patch
zswap-dynamic-pool-creation.patch
zswap-dynamic-pool-creation-fix-2.patch
zswap-change-zpool-compressor-at-runtime.patch
zswap-change-zpool-compressor-at-runtime-fix.patch
zswap-update-docs-for-runtime-changeable-attributes.patch
zswap-update-docs-for-runtime-changeable-attributes-v2.patch
zpool-remove-no-op-module-init-exit.patch
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