Acked-by: Chris Li <chrisl@xxxxxxxxxx>
Chris
On Thu, Feb 22, 2024 at 12:12 AM Barry Song <21cnbao@xxxxxxxxx> wrote:
>
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> Most compressors are actually CPU-based and won't sleep during
> compression and decompression. We should remove the redundant
> memcpy for them.
> This patch checks if the algorithm is sleepable by testing the
> CRYPTO_ALG_ASYNC algorithm flag.
> Generally speaking, async and sleepable are semantically similar
> but not equal. But for compress drivers, they are basically equal
> at least due to the below facts.
> Firstly, scompress drivers - crypto/deflate.c, lz4.c, zstd.c,
> lzo.c etc have no sleep. Secondly, zRAM has been using these
> scompress drivers for years in atomic contexts, and never
> worried those drivers going to sleep.
> One exception is that an async driver can sometimes still return
> synchronously per Herbert's clarification. In this case, we are
> still having a redundant memcpy. But we can't know if one
> particular acomp request will sleep or not unless crypto can
> expose more details for each specific request from offload
> drivers.
>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> Tested-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
> Acked-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Reviewed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> ---
> mm/zswap.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 011e068eb355..de3c9e30bed7 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -162,6 +162,7 @@ struct crypto_acomp_ctx {
> struct crypto_wait wait;
> u8 *buffer;
> struct mutex mutex;
> + bool is_sleepable;
> };
>
> /*
> @@ -950,6 +951,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
> goto acomp_fail;
> }
> acomp_ctx->acomp = acomp;
> + acomp_ctx->is_sleepable = acomp_is_async(acomp);
>
> req = acomp_request_alloc(acomp_ctx->acomp);
> if (!req) {
> @@ -1077,7 +1079,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
> mutex_lock(&acomp_ctx->mutex);
>
> src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> - if (!zpool_can_sleep_mapped(zpool)) {
> + if (acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) {
> memcpy(acomp_ctx->buffer, src, entry->length);
> src = acomp_ctx->buffer;
> zpool_unmap_handle(zpool, entry->handle);
> @@ -1091,7 +1093,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
> BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
> mutex_unlock(&acomp_ctx->mutex);
>
> - if (zpool_can_sleep_mapped(zpool))
> + if (!acomp_ctx->is_sleepable || zpool_can_sleep_mapped(zpool))
> zpool_unmap_handle(zpool, entry->handle);
> }
>
> --
> 2.34.1
>
