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mm: zswap: support exclusive loads

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Commit 71024cb4a0 ("frontswap: remove frontswap_tmem_exclusive_gets")
removed support for exclusive loads from frontswap as it was not used. 
Bring back exclusive loads support to frontswap by adding an "exclusive"
output parameter to frontswap_ops->load.

On the zswap side, add a module parameter to enable/disable exclusive
loads, and a config option to control the boot default value.  Refactor
zswap entry invalidation in zswap_frontswap_invalidate_page() into
zswap_invalidate_entry() to reuse it in zswap_frontswap_load() if
exclusive loads are enabled.

With exclusive loads, we avoid having two copies of the same page in
memory (compressed & uncompressed) after faulting it in from zswap.  On
the other hand, if the page is to be reclaimed again without being
dirtied, it will be re-compressed.  Compression is not usually slow, and a
page that was just faulted in is less likely to be reclaimed again soon.

Link: https://lkml.kernel.org/r/20230607195143.1473802-1-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Suggested-by: Yu Zhao <yuzhao@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yosry Ahmed 2023-06-07 19:51:43 +00:00 committed by Andrew Morton
parent 32b6a4a174
commit b9c91c4341
4 changed files with 45 additions and 11 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/frontswap.h
View file

@ -10,7 +10,7 @@
struct frontswap_ops {
void (*init)(unsigned); /* this swap type was just swapon'ed */
int (*store)(unsigned, pgoff_t, struct page *); /* store a page */
int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
int (*load)(unsigned, pgoff_t, struct page *, bool *); /* load a page */
void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
};

16
mm/Kconfig
View file

@ -46,6 +46,22 @@ config ZSWAP_DEFAULT_ON
The selection made here can be overridden by using the kernel
command line 'zswap.enabled=' option.
config ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON
bool "Invalidate zswap entries when pages are loaded"
depends on ZSWAP
help
If selected, exclusive loads for zswap will be enabled at boot,
otherwise it will be disabled.
If exclusive loads are enabled, when a page is loaded from zswap,
the zswap entry is invalidated at once, as opposed to leaving it
in zswap until the swap entry is freed.
This avoids having two copies of the same page in memory
(compressed and uncompressed) after faulting in a page from zswap.
The cost is that if the page was never dirtied and needs to be
swapped out again, it will be re-compressed.
choice
prompt "Default compressor"
depends on ZSWAP

10
mm/frontswap.c
View file

@ -206,6 +206,7 @@ int __frontswap_load(struct page *page)
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
bool exclusive = false;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
@ -215,9 +216,14 @@ int __frontswap_load(struct page *page)
return -1;
/* Try loading from each implementation, until one succeeds. */
ret = frontswap_ops->load(type, offset, page);
if (ret == 0)
ret = frontswap_ops->load(type, offset, page, &exclusive);
if (ret == 0) {
inc_frontswap_loads();
if (exclusive) {
SetPageDirty(page);
__frontswap_clear(sis, offset);
}
}
return ret;
}

28
mm/zswap.c
View file

@ -138,6 +138,10 @@ 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);
static bool zswap_exclusive_loads_enabled = IS_ENABLED(
CONFIG_ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON);
module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644);
/*********************************
* data structures
**********************************/
@ -1340,12 +1344,22 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
goto reject;
}
static void zswap_invalidate_entry(struct zswap_tree *tree,
struct zswap_entry *entry)
{
/* remove from rbtree */
zswap_rb_erase(&tree->rbroot, entry);
/* drop the initial reference from entry creation */
zswap_entry_put(tree, entry);
}
/*
* returns 0 if the page was successfully decompressed
* return -1 on entry not found or error
*/
static int zswap_frontswap_load(unsigned type, pgoff_t offset,
struct page *page)
struct page *page, bool *exclusive)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry;
@ -1415,6 +1429,10 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
freeentry:
spin_lock(&tree->lock);
zswap_entry_put(tree, entry);
if (!ret && zswap_exclusive_loads_enabled) {
zswap_invalidate_entry(tree, entry);
*exclusive = true;
}
spin_unlock(&tree->lock);
return ret;
@ -1434,13 +1452,7 @@ static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
spin_unlock(&tree->lock);
return;
}
/* remove from rbtree */
zswap_rb_erase(&tree->rbroot, entry);
/* drop the initial reference from entry creation */
zswap_entry_put(tree, entry);
zswap_invalidate_entry(tree, entry);
spin_unlock(&tree->lock);
}