mm: free up PG_slab

Reclaim the Slab page flag by using a spare bit in PageType.  We are
perennially short of page flags for various purposes, and now that the
original SLAB allocator has been retired, SLUB does not use the
mapcount/page_type field.  This lets us remove a number of special cases
for ignoring mapcount on Slab pages.

[willy@infradead.org: update vmcoreinfo]
Link: https://lkml.kernel.org/r/ZgGV-O8WYQ_83kxp@casper.infradead.org
Link: https://lkml.kernel.org/r/20240321142448.1645400-8-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 94eb8a11a321289c949ecfed9e75fc0c0ab76216..73e0b17c77283f2426498f6e25094c7b3273174f 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -109,7 +109,6 @@ enum pageflags {
        PG_active,
        PG_workingset,
        PG_error,
-       PG_slab,
        PG_owner_priv_1,        /* Owner use. If pagecache, fs may use*/
        PG_arch_1,
        PG_reserved,
@@ -524,7 +523,6 @@ PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
        TESTCLEARFLAG(Active, active, PF_HEAD)
 PAGEFLAG(Workingset, workingset, PF_HEAD)
        TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
-__PAGEFLAG(Slab, slab, PF_NO_TAIL)
 PAGEFLAG(Checked, checked, PF_NO_COMPOUND)        /* Used by some filesystems */
 
 /* Xen */
@@ -931,7 +929,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
 #endif
 
 /*
- * For pages that are never mapped to userspace (and aren't PageSlab),
+ * For pages that are never mapped to userspace,
  * page_type may be used.  Because it is initialised to -1, we invert the
  * sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and
  * __ClearPageFoo *sets* the bit used for PageFoo.  We reserve a few high and
@@ -947,6 +945,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
 #define PG_table       0x00000200
 #define PG_guard       0x00000400
 #define PG_hugetlb     0x00000800
+#define PG_slab                0x00001000
 
 #define PageType(page, flag)                                           \
        ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -1041,6 +1040,20 @@ PAGE_TYPE_OPS(Table, table, pgtable)
  */
 PAGE_TYPE_OPS(Guard, guard, guard)
 
+FOLIO_TYPE_OPS(slab, slab)
+
+/**
+ * PageSlab - Determine if the page belongs to the slab allocator
+ * @page: The page to test.
+ *
+ * Context: Any context.
+ * Return: True for slab pages, false for any other kind of page.
+ */
+static inline bool PageSlab(const struct page *page)
+{
+       return folio_test_slab(page_folio(page));
+}
+
 #ifdef CONFIG_HUGETLB_PAGE
 FOLIO_TYPE_OPS(hugetlb, hugetlb)
 #else
@@ -1121,7 +1134,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
        (1UL << PG_lru          | 1UL << PG_locked      |       \
         1UL << PG_private      | 1UL << PG_private_2   |       \
         1UL << PG_writeback    | 1UL << PG_reserved    |       \
-        1UL << PG_slab         | 1UL << PG_active      |       \
+        1UL << PG_active       |                               \
         1UL << PG_unevictable  | __PG_MLOCKED | LRU_GEN_MASK)
 
 /*

diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index d55e53ac91bd2cbb3cc24836a96a4d38af752c9d..e46d6e82765e7155fbbf63564315789efefbb3ac 100644 (file)
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -107,7 +107,6 @@
        DEF_PAGEFLAG_NAME(lru),                                         \
        DEF_PAGEFLAG_NAME(active),                                      \
        DEF_PAGEFLAG_NAME(workingset),                                  \
-       DEF_PAGEFLAG_NAME(slab),                                        \
        DEF_PAGEFLAG_NAME(owner_priv_1),                                \
        DEF_PAGEFLAG_NAME(arch_1),                                      \
        DEF_PAGEFLAG_NAME(reserved),                                    \
@@ -135,6 +134,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
 #define DEF_PAGETYPE_NAME(_name) { PG_##_name, __stringify(_name) }
 
 #define __def_pagetype_names                                           \
+       DEF_PAGETYPE_NAME(slab),                                        \
        DEF_PAGETYPE_NAME(hugetlb),                                     \
        DEF_PAGETYPE_NAME(offline),                                     \
        DEF_PAGETYPE_NAME(guard),                                       \

diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
index 23c125c2e2436c935a6e35b256d81866777ef35e..1d5eadd9dd61cde1162e810425dfc1814b116eeb 100644 (file)
--- a/kernel/vmcore_info.c
+++ b/kernel/vmcore_info.c
@@ -198,7 +198,8 @@ static int __init crash_save_vmcoreinfo_init(void)
        VMCOREINFO_NUMBER(PG_private);
        VMCOREINFO_NUMBER(PG_swapcache);
        VMCOREINFO_NUMBER(PG_swapbacked);
-       VMCOREINFO_NUMBER(PG_slab);
+#define PAGE_SLAB_MAPCOUNT_VALUE       (~PG_slab)
+       VMCOREINFO_NUMBER(PAGE_SLAB_MAPCOUNT_VALUE);
 #ifdef CONFIG_MEMORY_FAILURE
        VMCOREINFO_NUMBER(PG_hwpoison);
 #endif

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 9e62a00b46ddee5899f85cfc252dabd7c0d04121..0a7a8a4ba421d507b2d0263b791b7d45e86e6f3a 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1251,7 +1251,6 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 #define mlock          (1UL << PG_mlocked)
 #define lru            (1UL << PG_lru)
 #define head           (1UL << PG_head)
-#define slab           (1UL << PG_slab)
 #define reserved       (1UL << PG_reserved)
 
 static struct page_state error_states[] = {
@@ -1261,13 +1260,6 @@ static struct page_state error_states[] = {
         * PG_buddy pages only make a small fraction of all free pages.
         */
 
-       /*
-        * Could in theory check if slab page is free or if we can drop
-        * currently unused objects without touching them. But just
-        * treat it as standard kernel for now.
-        */
-       { slab,         slab,           MF_MSG_SLAB,    me_kernel },
-
        { head,         head,           MF_MSG_HUGE,            me_huge_page },
 
        { sc|dirty,     sc|dirty,       MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
@@ -1294,7 +1286,6 @@ static struct page_state error_states[] = {
 #undef mlock
 #undef lru
 #undef head
-#undef slab
 #undef reserved
 
 static void update_per_node_mf_stats(unsigned long pfn,

diff --git a/mm/slab.h b/mm/slab.h
index 65db525e93af38438219ae2f510261bef581e59d..1343bfa12cee95b01464f7a3c17f91de82832b01 100644 (file)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -84,8 +84,8 @@ struct slab {
                };
                struct rcu_head rcu_head;
        };
-       unsigned int __unused;
 
+       unsigned int __page_type;
        atomic_t __page_refcount;
 #ifdef CONFIG_SLAB_OBJ_EXT
        unsigned long obj_exts;