On Mon, Jan 8, 2018 at 5:51 PM, Yu Zhao <yuzhao@xxxxxxxxxx> wrote:
> We waste sizeof(swp_entry_t) for zswap header when using zsmalloc
> as zpool driver because zsmalloc doesn't support eviction.
>
> Add zpool_shrinkable() to detect if zpool is shrinkable, and use
> it in zswap to avoid waste memory for zswap header.
>
> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> ---
> include/linux/zpool.h | 2 ++
> mm/zpool.c | 17 ++++++++++++++++-
> mm/zsmalloc.c | 7 -------
> mm/zswap.c | 20 ++++++++++----------
> 4 files changed, 28 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> index 004ba807df96..3f0ac2ab74aa 100644
> --- a/include/linux/zpool.h
> +++ b/include/linux/zpool.h
> @@ -108,4 +108,6 @@ void zpool_register_driver(struct zpool_driver *driver);
>
> int zpool_unregister_driver(struct zpool_driver *driver);
>
> +bool zpool_shrinkable(struct zpool *pool);
> +
> #endif
> diff --git a/mm/zpool.c b/mm/zpool.c
> index fd3ff719c32c..839d4234c540 100644
> --- a/mm/zpool.c
> +++ b/mm/zpool.c
> @@ -296,7 +296,8 @@ 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_shrinkable(zpool) ?
> + zpool->driver->shrink(zpool->pool, pages, reclaimed) : -EINVAL;
> }
>
> /**
> @@ -355,6 +356,20 @@ u64 zpool_get_total_size(struct zpool *zpool)
> return zpool->driver->total_size(zpool->pool);
> }
>
> +/**
> + * zpool_shrinkable() - Test if zpool is shrinkable
> + * @pool The zpool to test
> + *
> + * Zpool is only shrinkable when it's created with struct
> + * zpool_ops.evict and its driver implements struct zpool_driver.shrink.
> + *
> + * Returns: true if shrinkable; false otherwise.
> + */
> +bool zpool_shrinkable(struct zpool *zpool)
> +{
> + return zpool->ops && zpool->ops->evict && zpool->driver->shrink;
as these things won't ever change for the life of the zpool, it would
probably be better to just check them at zpool creation time and set a
single new zpool param, like 'zpool->shrinkable'. since this function
will be called for every page that's swapped in or out, that may save
a bit of time.
also re: calling it 'shrinkable' or 'evictable', the real thing zswap
is interested in is if it needs to include the header info that
zswap_writeback_entry (i.e. ops->evict) later needs, so yeah it does
make more sense to call it zpool_evictable() and zpool->evictable.
However, I think the function should still be zpool_shrink() and
zpool->driver->shrink(), because it should be possible for
zs_pool_shrink() to call the normal zsmalloc shrinker, instead of
doing the zswap-style eviction, even if it doesn't do that currently.
> +}
> +
> MODULE_LICENSE("GPL");
> MODULE_AUTHOR("Dan Streetman <ddstreet@xxxxxxxx>");
> MODULE_DESCRIPTION("Common API for compressed memory storage");
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 683c0651098c..9cc741bcdb32 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -407,12 +407,6 @@ static void zs_zpool_free(void *pool, unsigned long handle)
> zs_free(pool, handle);
> }
>
> -static int zs_zpool_shrink(void *pool, unsigned int pages,
> - unsigned int *reclaimed)
> -{
> - return -EINVAL;
> -}
> -
> static void *zs_zpool_map(void *pool, unsigned long handle,
> enum zpool_mapmode mm)
> {
> @@ -450,7 +444,6 @@ static struct zpool_driver zs_zpool_driver = {
> .destroy = zs_zpool_destroy,
> .malloc = zs_zpool_malloc,
> .free = zs_zpool_free,
> - .shrink = zs_zpool_shrink,
> .map = zs_zpool_map,
> .unmap = zs_zpool_unmap,
> .total_size = zs_zpool_total_size,
> diff --git a/mm/zswap.c b/mm/zswap.c
> index d39581a076c3..15d2ea29a6fa 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -964,11 +964,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> struct zswap_entry *entry, *dupentry;
> struct crypto_comp *tfm;
> int ret;
> - unsigned int dlen = PAGE_SIZE, len;
> + unsigned int hlen, dlen = PAGE_SIZE;
> unsigned long handle;
> char *buf;
> u8 *src, *dst;
> - struct zswap_header *zhdr;
> + struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) };
>
> if (!zswap_enabled || !tree) {
> ret = -ENODEV;
> @@ -1013,8 +1013,8 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> }
>
> /* store */
> - len = dlen + sizeof(struct zswap_header);
> - ret = zpool_malloc(entry->pool->zpool, len,
> + hlen = zpool_shrinkable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> + ret = zpool_malloc(entry->pool->zpool, hlen + dlen,
> __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM,
> &handle);
> if (ret == -ENOSPC) {
> @@ -1025,10 +1025,9 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> zswap_reject_alloc_fail++;
> goto put_dstmem;
> }
> - zhdr = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_RW);
> - zhdr->swpentry = swp_entry(type, offset);
> - buf = (u8 *)(zhdr + 1);
> - memcpy(buf, dst, dlen);
> + buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_RW);
> + memcpy(buf, &zhdr, hlen);
> + memcpy(buf + hlen, dst, dlen);
> zpool_unmap_handle(entry->pool->zpool, handle);
> put_cpu_var(zswap_dstmem);
>
> @@ -1091,8 +1090,9 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>
> /* decompress */
> dlen = PAGE_SIZE;
> - src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle,
> - ZPOOL_MM_RO) + sizeof(struct zswap_header);
> + src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> + if (zpool_shrinkable(entry->pool->zpool))
> + src += sizeof(struct zswap_header);
> dst = kmap_atomic(page);
> tfm = *get_cpu_ptr(entry->pool->tfm);
> ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen);
> --
> 2.16.0.rc0.223.g4a4ac83678-goog
>
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