zsmalloc uses PG_private to indicate first zpdesc in a zspage chain. It is equivalent to check zpdesc == zspage->first_zpdesc. Replace is_first_zpdesc() with zpdesc == zspage->first_zpdesc in obj_allocated(). For get_first_zpdesc(), first_zpdesc is from zspage->first_zpdesc, so replace is_first_zpdesc() with first_zpdesc->zspage == zspage, the second requirement of a zspage chain, where all zpdescs point to the same zspage. is_first_zpdesc(), is only used in VM_BUG_ON_PAGE(), so performance impact should be negligible. While at it, change VM_BUG_ON() to VM_WARN_ON_ONCE_PAGE(). It prepares for a future commit that remove PG_private. No functional change intended. Assisted-by: Claude:claude-opus-4-8 Assisted-by: Codex:gpt-5 To: Minchan Kim To: Sergey Senozhatsky To: Andrew Morton Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Acked-by: Johannes Weiner Signed-off-by: Zi Yan --- mm/zpdesc.h | 2 +- mm/zsmalloc.c | 24 ++++++------------------ 2 files changed, 7 insertions(+), 19 deletions(-) diff --git a/mm/zpdesc.h b/mm/zpdesc.h index b8258dc78548d..4fd81c2e80769 100644 --- a/mm/zpdesc.h +++ b/mm/zpdesc.h @@ -26,8 +26,8 @@ * with memcg_data. * * Page flags used: - * * PG_private identifies the first component page. * * PG_locked is used by page migration code. + * The first component page has zpdesc->zspage->first_zpdesc == zpdesc */ struct zpdesc { unsigned long flags; diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 825022a7a328f..24526185fd31f 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -290,11 +290,6 @@ struct zs_pool { atomic_t compaction_in_progress; }; -static inline void zpdesc_set_first(struct zpdesc *zpdesc) -{ - SetPagePrivate(zpdesc_page(zpdesc)); -} - static inline void zpdesc_inc_zone_page_state(struct zpdesc *zpdesc) { inc_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES); @@ -476,11 +471,6 @@ static void record_obj(unsigned long handle, unsigned long obj) WRITE_ONCE(*(unsigned long *)handle, obj); } -static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc) -{ - return PagePrivate(zpdesc_page(zpdesc)); -} - /* Protected by class->lock */ static inline int get_zspage_inuse(struct zspage *zspage) { @@ -496,7 +486,8 @@ static struct zpdesc *get_first_zpdesc(struct zspage *zspage) { struct zpdesc *first_zpdesc = zspage->first_zpdesc; - VM_BUG_ON_PAGE(!is_first_zpdesc(first_zpdesc), zpdesc_page(first_zpdesc)); + /* the first zpdesc must point back to this zspage */ + VM_WARN_ON_ONCE_PAGE(first_zpdesc->zspage != zspage, zpdesc_page(first_zpdesc)); return first_zpdesc; } @@ -838,7 +829,8 @@ static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj, struct zspage *zspage = get_zspage(zpdesc); if (unlikely(ZsHugePage(zspage))) { - VM_BUG_ON_PAGE(!is_first_zpdesc(zpdesc), zpdesc_page(zpdesc)); + /* only first zpdesc holds the handle */ + VM_WARN_ON_ONCE_PAGE(zspage->first_zpdesc != zpdesc, zpdesc_page(zpdesc)); handle = zpdesc->handle; } else handle = *(unsigned long *)obj; @@ -853,9 +845,6 @@ static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj, static void reset_zpdesc(struct zpdesc *zpdesc) { - struct page *page = zpdesc_page(zpdesc); - - ClearPagePrivate(page); zpdesc->zspage = NULL; zpdesc->next = NULL; /* PageZsmalloc is sticky until the page is freed to the buddy. */ @@ -1006,8 +995,8 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage, * 1. all pages are linked together using zpdesc->next * 2. each sub-page point to zspage using zpdesc->zspage * - * we set PG_private to identify the first zpdesc (i.e. no other zpdesc - * has this flag set). + * The first zpdesc has its zspage->first_zpdesc set to itself, no + * other zpdesc has this set. */ for (i = 0; i < nr_zpdescs; i++) { zpdesc = zpdescs[i]; @@ -1015,7 +1004,6 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage, zpdesc->next = NULL; if (i == 0) { zspage->first_zpdesc = zpdesc; - zpdesc_set_first(zpdesc); if (unlikely(class->objs_per_zspage == 1 && class->pages_per_zspage == 1)) SetZsHugePage(zspage); -- 2.53.0