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Message-ID: <Z5zwcPBAY7JaVW6Z@google.com>
Date: Fri, 31 Jan 2025 15:46:56 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 12/17] zsmalloc: factor out pool locking helpers
On Fri, Jan 31, 2025 at 06:06:11PM +0900, Sergey Senozhatsky wrote:
> We currently have a mix of migrate_{read,write}_lock() helpers
> that lock zspages, but it's zs_pool that actually has a ->migrate_lock
> access to which is opene-coded. Factor out pool migrate locking
> into helpers, zspage migration locking API will be renamed to
> reduce confusion.
>
> It's worth mentioning that zsmalloc locks sync not only migration,
> but also compaction.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>
> ---
> mm/zsmalloc.c | 69 +++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 47 insertions(+), 22 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 817626a351f8..c129596ab960 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -18,7 +18,7 @@
> /*
> * lock ordering:
> * page_lock
> - * pool->migrate_lock
> + * pool->lock
> * class->lock
> * zspage->lock
> */
> @@ -224,10 +224,35 @@ struct zs_pool {
> struct work_struct free_work;
> #endif
> /* protect page/zspage migration */
> - rwlock_t migrate_lock;
> + rwlock_t lock;
> atomic_t compaction_in_progress;
> };
>
> +static void pool_write_unlock(struct zs_pool *pool)
> +{
> + write_unlock(&pool->lock);
> +}
> +
> +static void pool_write_lock(struct zs_pool *pool)
> +{
> + write_lock(&pool->lock);
> +}
> +
> +static void pool_read_unlock(struct zs_pool *pool)
> +{
> + read_unlock(&pool->lock);
> +}
> +
> +static void pool_read_lock(struct zs_pool *pool)
> +{
> + read_lock(&pool->lock);
> +}
> +
> +static bool pool_lock_is_contended(struct zs_pool *pool)
> +{
> + return rwlock_is_contended(&pool->lock);
> +}
> +
> static inline void zpdesc_set_first(struct zpdesc *zpdesc)
> {
> SetPagePrivate(zpdesc_page(zpdesc));
> @@ -290,7 +315,7 @@ static bool ZsHugePage(struct zspage *zspage)
> return zspage->huge;
> }
>
> -static void migrate_lock_init(struct zspage *zspage);
> +static void lock_init(struct zspage *zspage);
Seems like this change slipped in here, with a s/migrate_lock/lock
replacement if I have to make a guess :P
> static void migrate_read_lock(struct zspage *zspage);
> static void migrate_read_unlock(struct zspage *zspage);
> static void migrate_write_lock(struct zspage *zspage);
> @@ -992,7 +1017,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
> return NULL;
>
> zspage->magic = ZSPAGE_MAGIC;
> - migrate_lock_init(zspage);
> + lock_init(zspage);
>
> for (i = 0; i < class->pages_per_zspage; i++) {
> struct zpdesc *zpdesc;
> @@ -1206,7 +1231,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> BUG_ON(in_interrupt());
>
> /* It guarantees it can get zspage from handle safely */
> - read_lock(&pool->migrate_lock);
> + pool_read_lock(pool);
> obj = handle_to_obj(handle);
> obj_to_location(obj, &zpdesc, &obj_idx);
> zspage = get_zspage(zpdesc);
> @@ -1218,7 +1243,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> * which is smaller granularity.
> */
> migrate_read_lock(zspage);
> - read_unlock(&pool->migrate_lock);
> + pool_read_unlock(pool);
>
> class = zspage_class(pool, zspage);
> off = offset_in_page(class->size * obj_idx);
> @@ -1450,16 +1475,16 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
> return;
>
> /*
> - * The pool->migrate_lock protects the race with zpage's migration
> + * The pool->lock protects the race with zpage's migration
> * so it's safe to get the page from handle.
> */
> - read_lock(&pool->migrate_lock);
> + pool_read_lock(pool);
> obj = handle_to_obj(handle);
> obj_to_zpdesc(obj, &f_zpdesc);
> zspage = get_zspage(f_zpdesc);
> class = zspage_class(pool, zspage);
> spin_lock(&class->lock);
> - read_unlock(&pool->migrate_lock);
> + pool_read_unlock(pool);
>
> class_stat_sub(class, ZS_OBJS_INUSE, 1);
> obj_free(class->size, obj);
> @@ -1703,7 +1728,7 @@ static void lock_zspage(struct zspage *zspage)
> }
> #endif /* CONFIG_COMPACTION */
>
> -static void migrate_lock_init(struct zspage *zspage)
> +static void lock_init(struct zspage *zspage)
> {
> rwlock_init(&zspage->lock);
> }
> @@ -1793,10 +1818,10 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
> pool = zspage->pool;
>
> /*
> - * The pool migrate_lock protects the race between zpage migration
> + * The pool lock protects the race between zpage migration
> * and zs_free.
> */
> - write_lock(&pool->migrate_lock);
> + pool_write_lock(pool);
> class = zspage_class(pool, zspage);
>
> /*
> @@ -1833,7 +1858,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
> * Since we complete the data copy and set up new zspage structure,
> * it's okay to release migration_lock.
> */
> - write_unlock(&pool->migrate_lock);
> + pool_write_unlock(pool);
> spin_unlock(&class->lock);
> migrate_write_unlock(zspage);
>
> @@ -1956,7 +1981,7 @@ static unsigned long __zs_compact(struct zs_pool *pool,
> * protect the race between zpage migration and zs_free
> * as well as zpage allocation/free
> */
> - write_lock(&pool->migrate_lock);
> + pool_write_lock(pool);
> spin_lock(&class->lock);
> while (zs_can_compact(class)) {
> int fg;
> @@ -1983,14 +2008,14 @@ static unsigned long __zs_compact(struct zs_pool *pool,
> src_zspage = NULL;
>
> if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
> - || rwlock_is_contended(&pool->migrate_lock)) {
> + || pool_lock_is_contended(pool)) {
> putback_zspage(class, dst_zspage);
> dst_zspage = NULL;
>
> spin_unlock(&class->lock);
> - write_unlock(&pool->migrate_lock);
> + pool_write_unlock(pool);
> cond_resched();
> - write_lock(&pool->migrate_lock);
> + pool_write_lock(pool);
> spin_lock(&class->lock);
> }
> }
> @@ -2002,7 +2027,7 @@ static unsigned long __zs_compact(struct zs_pool *pool,
> putback_zspage(class, dst_zspage);
>
> spin_unlock(&class->lock);
> - write_unlock(&pool->migrate_lock);
> + pool_write_unlock(pool);
>
> return pages_freed;
> }
> @@ -2014,10 +2039,10 @@ unsigned long zs_compact(struct zs_pool *pool)
> unsigned long pages_freed = 0;
>
> /*
> - * Pool compaction is performed under pool->migrate_lock so it is basically
> + * Pool compaction is performed under pool->lock so it is basically
> * single-threaded. Having more than one thread in __zs_compact()
> - * will increase pool->migrate_lock contention, which will impact other
> - * zsmalloc operations that need pool->migrate_lock.
> + * will increase pool->lock contention, which will impact other
> + * zsmalloc operations that need pool->lock.
> */
> if (atomic_xchg(&pool->compaction_in_progress, 1))
> return 0;
> @@ -2139,7 +2164,7 @@ struct zs_pool *zs_create_pool(const char *name)
> return NULL;
>
> init_deferred_free(pool);
> - rwlock_init(&pool->migrate_lock);
> + rwlock_init(&pool->lock);
> atomic_set(&pool->compaction_in_progress, 0);
>
> pool->name = kstrdup(name, GFP_KERNEL);
> --
> 2.48.1.362.g079036d154-goog
>
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