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Currently, zsmalloc performs address linearization on read (which sometimes requires memcpy() to a local buffer). Not all zsmalloc users need a linear address. For example, Crypto API supports SG-list, performing linearization under the hood, if needed. In addition, some compressors can have native SG-list support, completely avoiding the linearization step. Provide an SG-list based zsmalloc read API: - zs_obj_read_sg_begin() - zs_obj_read_sg_end() This API allows callers to obtain an SG representation of the object (one entry for objects that are contained in a single page and two entries for spanning objects), avoiding the need for a bounce buffer and memcpy. [senozhatsky@chromium.org: make zs_obj_read_sg_begin() return void, per Yosry] Link: https://lkml.kernel.org/r/20260117024900.792237-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20260113034645.2729998-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Tested-by: Yosry Ahmed <yosry.ahmed@linux.dev> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Brian Geffon <bgeffon@google.com> 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>