On Fri, Dec 25, 2020 at 07:02:50PM +0800, Tian Tao wrote:
> add a flag to zpool, named is "can_sleep_mapped", and have it set true
> for zbud/z3fold, set false for zsmalloc. Then zswap could go the current
> path if the flag is true; and if it's false, copy data from src to a
> temporary buffer, then unmap the handle, take the mutex, process the
> buffer instead of src to avoid sleeping function called from atomic
> context.
>
> Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
> ---
> include/linux/zpool.h | 3 +++
> mm/zpool.c | 13 +++++++++++++
> mm/zswap.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
> 3 files changed, 61 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> index 51bf430..e899701 100644
> --- a/include/linux/zpool.h
> +++ b/include/linux/zpool.h
> @@ -73,6 +73,7 @@ u64 zpool_get_total_size(struct zpool *pool);
> * @malloc: allocate mem from a pool.
> * @free: free mem from a pool.
> * @shrink: shrink the pool.
> + * @sleep_mapped: whether zpool driver can sleep during map.
I don't think it's a good idea. It just breaks zpool abstraction
in that it exposes internal implementation to user to avoid issue
zswap recently introduced. It also conflicts zpool_map_handle's
semantic.
Rather than introducing another break in zpool due to the new
zswap feature recenlty introduced, zswap could introduce
CONFIG_ZSWAP_HW_COMPRESSOR. Once it's configured, zsmalloc could
be disabled. And with disabling CONFIG_ZSWAP_HW_COMPRESSOR, zswap
doesn't need to make any bounce buffer copy so that no existing
zsmalloc user will see performance regression.
> * @map: map a handle.
> * @unmap: unmap a handle.
> * @total_size: get total size of a pool.
> @@ -100,6 +101,7 @@ struct zpool_driver {
> int (*shrink)(void *pool, unsigned int pages,
> unsigned int *reclaimed);
>
> + bool sleep_mapped;
> void *(*map)(void *pool, unsigned long handle,
> enum zpool_mapmode mm);
> void (*unmap)(void *pool, unsigned long handle);
> @@ -112,5 +114,6 @@ void zpool_register_driver(struct zpool_driver *driver);
> int zpool_unregister_driver(struct zpool_driver *driver);
>
> bool zpool_evictable(struct zpool *pool);
> +bool zpool_can_sleep_mapped(struct zpool *pool);
>
> #endif
> diff --git a/mm/zpool.c b/mm/zpool.c
> index 3744a2d..5ed7120 100644
> --- a/mm/zpool.c
> +++ b/mm/zpool.c
> @@ -23,6 +23,7 @@ struct zpool {
> void *pool;
> const struct zpool_ops *ops;
> bool evictable;
> + bool can_sleep_mapped;
>
> struct list_head list;
> };
> @@ -183,6 +184,7 @@ struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
> zpool->pool = driver->create(name, gfp, ops, zpool);
> zpool->ops = ops;
> zpool->evictable = driver->shrink && ops && ops->evict;
> + zpool->can_sleep_mapped = driver->sleep_mapped;
>
> if (!zpool->pool) {
> pr_err("couldn't create %s pool\n", type);
> @@ -393,6 +395,17 @@ bool zpool_evictable(struct zpool *zpool)
> return zpool->evictable;
> }
>
> +/**
> + * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
> + * @zpool: The zpool to test
> + *
> + * Returns: true if zpool can sleep; false otherwise.
> + */
> +bool zpool_can_sleep_mapped(struct zpool *zpool)
> +{
> + return zpool->can_sleep_mapped;
> +}
> +
> MODULE_LICENSE("GPL");
> MODULE_AUTHOR("Dan Streetman <ddstreet@xxxxxxxx>");
> MODULE_DESCRIPTION("Common API for compressed memory storage");
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 182f6ad..67d4555 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -935,13 +935,20 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> struct scatterlist input, output;
> struct crypto_acomp_ctx *acomp_ctx;
>
> - u8 *src;
> + u8 *src, *tmp;
> unsigned int dlen;
> int ret;
> struct writeback_control wbc = {
> .sync_mode = WB_SYNC_NONE,
> };
>
> + if (!zpool_can_sleep_mapped(pool)) {
> +
> + tmp = kmalloc(entry->length, GFP_ATOMIC);
> + if (!tmp)
> + return -ENOMEM;
> + }
> +
> /* extract swpentry from data */
> zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
> swpentry = zhdr->swpentry; /* here */
> @@ -979,6 +986,14 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> dlen = PAGE_SIZE;
> src = (u8 *)zhdr + sizeof(struct zswap_header);
>
> + if (!zpool_can_sleep_mapped(pool)) {
> +
> + memcpy(tmp, src, entry->length);
> + src = tmp;
> +
> + zpool_unmap_handle(pool, handle);
> + }
> +
> mutex_lock(acomp_ctx->mutex);
> sg_init_one(&input, src, entry->length);
> sg_init_table(&output, 1);
> @@ -1033,7 +1048,11 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> spin_unlock(&tree->lock);
>
> end:
> - zpool_unmap_handle(pool, handle);
> + if (zpool_can_sleep_mapped(pool))
> + zpool_unmap_handle(pool, handle);
> + else
> + kfree(tmp);
> +
> return ret;
> }
>
> @@ -1235,7 +1254,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> struct zswap_entry *entry;
> struct scatterlist input, output;
> struct crypto_acomp_ctx *acomp_ctx;
> - u8 *src, *dst;
> + u8 *src, *dst, *tmp;
> unsigned int dlen;
> int ret;
>
> @@ -1256,12 +1275,29 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> goto freeentry;
> }
>
> + if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> +
> + tmp = kmalloc(entry->length, GFP_ATOMIC);
> + if (!tmp) {
> + ret = -ENOMEM;
> + goto freeentry;
> + }
> + }
> +
> /* decompress */
> dlen = PAGE_SIZE;
> src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> if (zpool_evictable(entry->pool->zpool))
> src += sizeof(struct zswap_header);
>
> + if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> +
> + memcpy(tmp, src, entry->length);
> + src = tmp;
> +
> + zpool_unmap_handle(entry->pool->zpool, entry->handle);
> + }
> +
> acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> mutex_lock(acomp_ctx->mutex);
> sg_init_one(&input, src, entry->length);
> @@ -1271,7 +1307,11 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
> mutex_unlock(acomp_ctx->mutex);
>
> - zpool_unmap_handle(entry->pool->zpool, entry->handle);
> + if (zpool_can_sleep_mapped(entry->pool->zpool))
> + zpool_unmap_handle(entry->pool->zpool, entry->handle);
> + else
> + kfree(tmp);
> +
> BUG_ON(ret);
>
> freeentry:
> @@ -1279,7 +1319,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> zswap_entry_put(tree, entry);
> spin_unlock(&tree->lock);
>
> - return 0;
> + return ret;
> }
>
> /* frees an entry in zswap */
> --
> 2.7.4
>
>
