zsmalloc: simplify read begin/end logic

zs_obj_read_begin() currently maps or copies the compressed object with
the prefix handle for !ZsHugePage case.  Make the logic clearer and
more efficient by moving the offset of the object in the page after the
prefix handle instead, only copying the actual object and avoiding the
need to adjust the returned address to account for the prefix.

Adjust the logic to detect spanning objects in zs_obj_read_end()
accordingly, slightly simplifying it by avoiding the need to account
for the handle in both the offset and the object size.

Link: https://lkml.kernel.org/r/20260107052145.3586917-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Co-developed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 119c196a287a72844af7e910eca7578bf735f3d5..cc3d9501ae2190ef8b42d068ead92c2428e10977 100644 (file)
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1088,7 +1088,7 @@ void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
        off = offset_in_page(class->size * obj_idx);
 
        if (!ZsHugePage(zspage))
-               mem_len += ZS_HANDLE_SIZE;
+               off += ZS_HANDLE_SIZE;
 
        if (off + mem_len <= PAGE_SIZE) {
                /* this object is contained entirely within a page */
@@ -1110,9 +1110,6 @@ void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
                                 0, sizes[1]);
        }
 
-       if (!ZsHugePage(zspage))
-               addr += ZS_HANDLE_SIZE;
-
        return addr;
 }
 EXPORT_SYMBOL_GPL(zs_obj_read_begin);
@@ -1133,11 +1130,9 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
        off = offset_in_page(class->size * obj_idx);
 
        if (!ZsHugePage(zspage))
-               mem_len += ZS_HANDLE_SIZE;
+               off += ZS_HANDLE_SIZE;
 
        if (off + mem_len <= PAGE_SIZE) {
-               if (!ZsHugePage(zspage))
-                       off += ZS_HANDLE_SIZE;
                handle_mem -= off;
                kunmap_local(handle_mem);
        }