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mm/zswap.c: allow handling just same-value filled pages 

Zswap has an ability to efficiently store same-value filled pages, which
can be turned on and off using the "same_filled_pages_enabled"
parameter.

However, there is currently no way to enable just this (lightweight)
functionality, while not making use of the whole compressed page storage
machinery.

Add a "non_same_filled_pages_enabled" parameter which allows disabling
handling of pages that aren't same-value filled.  This way zswap can be
run in such lightweight same-value filled pages only mode.

Link: https://lkml.kernel.org/r/7dbafa963e8bab43608189abbe2067f4b9287831.1641247624.git.maciej.szmigiero@oracle.com
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Maciej S. Szmigiero 2022-03-22 14:47:43 -07:00 committed by Linus Torvalds
parent bd55b0c2d6
commit cb325ddde5
2 changed files with 33 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
Documentation/admin-guide/mm/zswap.rst
View File

@ -130,9 +130,25 @@ attribute, e.g.::
echo 1 > /sys/module/zswap/parameters/same_filled_pages_enabled
When zswap same-filled page identification is disabled at runtime, it will stop
checking for the same-value filled pages during store operation. However, the
existing pages which are marked as same-value filled pages remain stored
unchanged in zswap until they are either loaded or invalidated.
checking for the same-value filled pages during store operation.
In other words, every page will be then considered non-same-value filled.
However, the existing pages which are marked as same-value filled pages remain
stored unchanged in zswap until they are either loaded or invalidated.
In some circumstances it might be advantageous to make use of just the zswap
ability to efficiently store same-filled pages without enabling the whole
compressed page storage.
In this case the handling of non-same-value pages by zswap (enabled by default)
can be disabled by setting the ``non_same_filled_pages_enabled`` attribute
to 0, e.g. ``zswap.non_same_filled_pages_enabled=0``.
It can also be enabled and disabled at runtime using the sysfs
``non_same_filled_pages_enabled`` attribute, e.g.::
echo 1 > /sys/module/zswap/parameters/non_same_filled_pages_enabled
Disabling both ``zswap.same_filled_pages_enabled`` and
``zswap.non_same_filled_pages_enabled`` effectively disables accepting any new
pages by zswap.
To prevent zswap from shrinking pool when zswap is full and there's a high
pressure on swap (this will result in flipping pages in and out zswap pool

15
mm/zswap.c
View File

@ -120,11 +120,19 @@ static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
uint, 0644);
/* Enable/disable handling same-value filled pages (enabled by default) */
/*
* Enable/disable handling same-value filled pages (enabled by default).
* If disabled every page is considered non-same-value filled.
*/
static bool zswap_same_filled_pages_enabled = true;
module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
bool, 0644);
/* Enable/disable handling non-same-value filled pages (enabled by default) */
static bool zswap_non_same_filled_pages_enabled = true;
module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
bool, 0644);
/*********************************
* data structures
**********************************/
@ -1147,6 +1155,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
kunmap_atomic(src);
}
if (!zswap_non_same_filled_pages_enabled) {
ret = -EINVAL;
goto freepage;
}
/* if entry is successfully added, it keeps the reference */
entry->pool = zswap_pool_current_get();
if (!entry->pool) {