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zsmalloc: introduce SG-list based object read API

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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>
This commit is contained in:
Sergey Senozhatsky 2026-01-13 12:46:45 +09:00 • committed by Andrew Morton
parent 737dfe7d95
commit dc2e4982cb
2 changed files with 67 additions and 0 deletions
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4
include/linux/zsmalloc.h
View file

@ -22,6 +22,7 @@ struct zs_pool_stats {
};
struct zs_pool;
struct scatterlist;
struct zs_pool *zs_create_pool(const char *name);
void zs_destroy_pool(struct zs_pool *pool);
@ -43,6 +44,9 @@ void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
size_t mem_len, void *local_copy);
void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
size_t mem_len, void *handle_mem);
void zs_obj_read_sg_begin(struct zs_pool *pool, unsigned long handle,
struct scatterlist *sg, size_t mem_len);
void zs_obj_read_sg_end(struct zs_pool *pool, unsigned long handle);
void zs_obj_write(struct zs_pool *pool, unsigned long handle,
void *handle_mem, size_t mem_len);

63
mm/zsmalloc.c
View file

@ -30,6 +30,7 @@
#include <linux/highmem.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/scatterlist.h>
#include <linux/spinlock.h>
#include <linux/sprintf.h>
#include <linux/shrinker.h>
@ -1141,6 +1142,68 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
}
EXPORT_SYMBOL_GPL(zs_obj_read_end);
void zs_obj_read_sg_begin(struct zs_pool *pool, unsigned long handle,
struct scatterlist *sg, size_t mem_len)
{
struct zspage *zspage;
struct zpdesc *zpdesc;
unsigned long obj, off;
unsigned int obj_idx;
struct size_class *class;
/* Guarantee we can get zspage from handle safely */
read_lock(&pool->lock);
obj = handle_to_obj(handle);
obj_to_location(obj, &zpdesc, &obj_idx);
zspage = get_zspage(zpdesc);
/* Make sure migration doesn't move any pages in this zspage */
zspage_read_lock(zspage);
read_unlock(&pool->lock);
class = zspage_class(pool, zspage);
off = offset_in_page(class->size * obj_idx);
if (!ZsHugePage(zspage))
off += ZS_HANDLE_SIZE;
if (off + mem_len <= PAGE_SIZE) {
/* this object is contained entirely within a page */
sg_init_table(sg, 1);
sg_set_page(sg, zpdesc_page(zpdesc), mem_len, off);
} else {
size_t sizes[2];
/* this object spans two pages */
sizes[0] = PAGE_SIZE - off;
sizes[1] = mem_len - sizes[0];
sg_init_table(sg, 2);
sg_set_page(sg, zpdesc_page(zpdesc), sizes[0], off);
zpdesc = get_next_zpdesc(zpdesc);
sg = sg_next(sg);
sg_set_page(sg, zpdesc_page(zpdesc), sizes[1], 0);
}
}
EXPORT_SYMBOL_GPL(zs_obj_read_sg_begin);
void zs_obj_read_sg_end(struct zs_pool *pool, unsigned long handle)
{
struct zspage *zspage;
struct zpdesc *zpdesc;
unsigned long obj;
unsigned int obj_idx;
obj = handle_to_obj(handle);
obj_to_location(obj, &zpdesc, &obj_idx);
zspage = get_zspage(zpdesc);
zspage_read_unlock(zspage);
}
EXPORT_SYMBOL_GPL(zs_obj_read_sg_end);
void zs_obj_write(struct zs_pool *pool, unsigned long handle,
void *handle_mem, size_t mem_len)
{