mm/page_ext: do not allocate space for page_ext->flags if not needed

There is 8 byte page_ext->flags field allocated per page whenever
CONFIG_PAGE_EXTENSION is enabled.  However, not every user of page_ext
uses flags.  Therefore, check whether flags is needed at least by one user
and if so allocate space for it.

For example when page_table_check is enabled, on a machine with 128G
of memory before the fix:

[    2.244288] allocated 536870912 bytes of page_ext
after the fix:
[    2.160154] allocated 268435456 bytes of page_ext

Also, add a kernel-doc comment before page_ext_operations that describes
the fields, and remove check if need() is set, as that is now a required
field.

[pasha.tatashin@soleen.com: address comments from Mike Rapoport]
Link: https://lkml.kernel.org/r/20230117202103.1412449-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20230113154253.92480-1-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 22be458..67314f6 100644 (file)
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -7,15 +7,33 @@
 #include <linux/stackdepot.h>
 
 struct pglist_data;
+
+/**
+ * struct page_ext_operations - per page_ext client operations
+ * @offset: Offset to the client's data within page_ext. Offset is returned to
+ *          the client by page_ext_init.
+ * @size: The size of the client data within page_ext.
+ * @need: Function that returns true if client requires page_ext.
+ * @init: (optional) Called to initialize client once page_exts are allocated.
+ * @need_shared_flags: True when client is using shared page_ext->flags
+ *                     field.
+ *
+ * Each Page Extension client must define page_ext_operations in
+ * page_ext_ops array.
+ */
 struct page_ext_operations {
        size_t offset;
        size_t size;
        bool (*need)(void);
        void (*init)(void);
+       bool need_shared_flags;
 };
 
 #ifdef CONFIG_PAGE_EXTENSION
 
+/*
+ * The page_ext_flags users must set need_shared_flags to true.
+ */
 enum page_ext_flags {
        PAGE_EXT_OWNER,
        PAGE_EXT_OWNER_ALLOCATED,

diff --git a/mm/page_ext.c b/mm/page_ext.c
index 4ee522f..e2c22ff 100644 (file)
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -71,6 +71,7 @@ static bool need_page_idle(void)
 }
 static struct page_ext_operations page_idle_ops __initdata = {
        .need = need_page_idle,
+       .need_shared_flags = true,
 };
 #endif
 
@@ -86,7 +87,7 @@ static struct page_ext_operations *page_ext_ops[] __initdata = {
 #endif
 };
 
-unsigned long page_ext_size = sizeof(struct page_ext);
+unsigned long page_ext_size;
 
 static unsigned long total_usage;
 static struct page_ext *lookup_page_ext(const struct page *page);
@@ -106,7 +107,16 @@ static bool __init invoke_need_callbacks(void)
        bool need = false;
 
        for (i = 0; i < entries; i++) {
-               if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
+               if (page_ext_ops[i]->need()) {
+                       if (page_ext_ops[i]->need_shared_flags) {
+                               page_ext_size = sizeof(struct page_ext);
+                               break;
+                       }
+               }
+       }
+
+       for (i = 0; i < entries; i++) {
+               if (page_ext_ops[i]->need()) {
                        page_ext_ops[i]->offset = page_ext_size;
                        page_ext_size += page_ext_ops[i]->size;
                        need = true;

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 2d27f53..f0553be 100644 (file)
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -99,6 +99,7 @@ struct page_ext_operations page_owner_ops = {
        .size = sizeof(struct page_owner),
        .need = need_page_owner,
        .init = init_page_owner,
+       .need_shared_flags = true,
 };
 
 static inline struct page_owner *get_page_owner(struct page_ext *page_ext)

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 93e633c..25d8610 100644 (file)
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -45,6 +45,7 @@ struct page_ext_operations page_table_check_ops = {
        .size = sizeof(struct page_table_check),
        .need = need_page_table_check,
        .init = init_page_table_check,
+       .need_shared_flags = false,
 };
 
 static struct page_table_check *get_page_table_check(struct page_ext *page_ext)