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Date: Thu, 11 Jan 2018 16:59:21 -0500
From: Dan Streetman <ddstreet@...e.org>
To: Yu Zhao <yuzhao@...gle.com>
Cc: Seth Jennings <sjenning@...hat.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Minchan Kim <minchan@...nel.org>,
Nitin Gupta <ngupta@...are.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] zswap: only save zswap header when necessary
On Wed, Jan 10, 2018 at 5:56 PM, Yu Zhao <yuzhao@...gle.com> wrote:
> 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.
>
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>
> ---
> include/linux/zpool.h | 2 ++
> mm/zpool.c | 25 +++++++++++++++++++++++--
> mm/zsmalloc.c | 7 -------
> mm/zswap.c | 20 ++++++++++----------
> 4 files changed, 35 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> index 004ba807df96..7238865e75b0 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_evictable(struct zpool *pool);
> +
> #endif
> diff --git a/mm/zpool.c b/mm/zpool.c
> index fd3ff719c32c..e1e7aa6d1d06 100644
> --- a/mm/zpool.c
> +++ b/mm/zpool.c
> @@ -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;
Since the ops->evict comes from zswap (and is never omitted), if we do
restore zs_zpool_shrink() in the future to call the zsmalloc shrinker
(and not do eviction), we'll have to add a driver->evictable bool to
check here as well.
But for now this is good, the zpools with driver->shrink do eviction,
zsmalloc doesn't do eviction and won't have driver->shrink.
Acked-by: Dan Streetman <ddstreet@...e.org>
Thanks!
>
> 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 <ddstreet@...e.org>");
> 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..52a9ab519ab2 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_evictable(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_evictable(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.rc1.238.g530d649a79-goog
>
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