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zswap: only save zswap header when necessary

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We waste sizeof(swp_entry_t) for zswap header when using zsmalloc as
zpool driver because zsmalloc doesn't support eviction.

Add zpool_evictable() to detect if zpool is potentially evictable, and
use it in zswap to avoid waste memory for zswap header.

[[email protected]: The zpool->" prefix is a result of copy & paste]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yu Zhao <[email protected]>
Acked-by: Dan Streetman <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Yu Zhao 2018-01-31 16:19:59 -08:00 • committed by Linus Torvalds
commit 9c3760eb80
4 changed files with 35 additions and 19 deletions
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25
mm/zpool.c
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@ -21,6 +21,7 @@ struct zpool {
struct zpool_driver *driver;
void *pool;
const struct zpool_ops *ops;
bool evictable;
struct list_head list;
};
@ -142,7 +143,7 @@ EXPORT_SYMBOL(zpool_has_pool);
*
* This creates a new zpool of the specified type. The gfp flags will be
* used when allocating memory, if the implementation supports it. If the
* ops param is NULL, then the created zpool will not be shrinkable.
* ops param is NULL, then the created zpool will not be evictable.
*
* Implementations must guarantee this to be thread-safe.
*
@ -180,6 +181,7 @@ struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
zpool->driver = driver;
zpool->pool = driver->create(name, gfp, ops, zpool);
zpool->ops = ops;
zpool->evictable = driver->shrink && ops && ops->evict;
if (!zpool->pool) {
pr_err("couldn't create %s pool\n", type);
@ -296,7 +298,8 @@ void zpool_free(struct zpool *zpool, unsigned long handle)
int zpool_shrink(struct zpool *zpool, unsigned int pages,
unsigned int *reclaimed)
{
return zpool->driver->shrink(zpool->pool, pages, reclaimed);
return zpool->driver->shrink ?
zpool->driver->shrink(zpool->pool, pages, reclaimed) : -EINVAL;
}
/**
@ -355,6 +358,24 @@ u64 zpool_get_total_size(struct zpool *zpool)
return zpool->driver->total_size(zpool->pool);
}
/**
* zpool_evictable() - Test if zpool is potentially evictable
* @pool The zpool to test
*
* Zpool is only potentially evictable when it's created with struct
* zpool_ops.evict and its driver implements struct zpool_driver.shrink.
*
* However, it doesn't necessarily mean driver will use zpool_ops.evict
* in its implementation of zpool_driver.shrink. It could do internal
* defragmentation instead.
*
* Returns: true if potentially evictable; false otherwise.
*/
bool zpool_evictable(struct zpool *zpool)
{
return zpool->evictable;
}
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Dan Streetman <[email protected]>");
MODULE_DESCRIPTION("Common API for compressed memory storage");