From: Vitaly Wool <vitalywool@xxxxxxxxx> Subject: zswap: do not map same object twice zswap_writeback_entry() maps a handle to read swpentry first, and then in the most common case it would map the same handle again. This is ok when zbud is the backend since its mapping callback is plain and simple, but it slows things down for z3fold. Since there's hardly a point in unmapping a handle _that_ fast as zswap_writeback_entry() does when it reads swpentry, the suggestion is to keep the handle mapped till the end. Link: http://lkml.kernel.org/r/20190916004640.b453167d3556c4093af4cf7d@xxxxxxxxx Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx> Reviewed-by: Dan Streetman <ddstreet@xxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> Cc: Seth Jennings <sjenning@xxxxxxxxxx> Cc: Vitaly Wool <vitalywool@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/zswap.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) --- a/mm/zswap.c~zswap-do-not-map-same-object-twice +++ a/mm/zswap.c @@ -856,7 +856,6 @@ static int zswap_writeback_entry(struct /* extract swpentry from data */ zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO); swpentry = zhdr->swpentry; /* here */ - zpool_unmap_handle(pool, handle); tree = zswap_trees[swp_type(swpentry)]; offset = swp_offset(swpentry); @@ -866,6 +865,7 @@ static int zswap_writeback_entry(struct if (!entry) { /* entry was invalidated */ spin_unlock(&tree->lock); + zpool_unmap_handle(pool, handle); return 0; } spin_unlock(&tree->lock); @@ -886,15 +886,13 @@ static int zswap_writeback_entry(struct case ZSWAP_SWAPCACHE_NEW: /* page is locked */ /* decompress */ dlen = PAGE_SIZE; - src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, - ZPOOL_MM_RO) + sizeof(struct zswap_header); + src = (u8 *)zhdr + 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); put_cpu_ptr(entry->pool->tfm); kunmap_atomic(dst); - zpool_unmap_handle(entry->pool->zpool, entry->handle); BUG_ON(ret); BUG_ON(dlen != PAGE_SIZE); @@ -940,6 +938,7 @@ fail: spin_unlock(&tree->lock); end: + zpool_unmap_handle(pool, handle); return ret; } _
