From 688fcbfc06e4fdfbb7e1d5a942a1460fe6379d2d Mon Sep 17 00:00:00 2001 From: Pengfei Li Date: Mon, 23 Sep 2019 15:36:39 -0700 Subject: mm/vmalloc: modify struct vmap_area to reduce its size Objective --------- The current implementation of struct vmap_area wasted space. After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words. Description ----------- 1) Pack "subtree_max_size", "vm" and "purge_list". This is no problem because A) "subtree_max_size" is only used when vmap_area is in "free" tree B) "vm" is only used when vmap_area is in "busy" tree C) "purge_list" is only used when vmap_area is in vmap_purge_list 2) Eliminate "flags". ;Since only one flag VM_VM_AREA is being used, and the same thing can be done by judging whether "vm" is NULL, then the "flags" can be eliminated. Link: http://lkml.kernel.org/r/20190716152656.12255-3-lpf.vector@gmail.com Signed-off-by: Pengfei Li Suggested-by: Uladzislau Rezki (Sony) Reviewed-by: Uladzislau Rezki (Sony) Cc: Hillf Danton Cc: Matthew Wilcox Cc: Michal Hocko Cc: Oleksiy Avramchenko Cc: Roman Gushchin Cc: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/vmalloc.h | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) (limited to 'include/linux/vmalloc.h') diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index dfa718ffdd4f..4e7809408073 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -53,15 +53,21 @@ struct vmap_area { unsigned long va_start; unsigned long va_end; - /* - * Largest available free size in subtree. - */ - unsigned long subtree_max_size; - unsigned long flags; struct rb_node rb_node; /* address sorted rbtree */ struct list_head list; /* address sorted list */ - struct llist_node purge_list; /* "lazy purge" list */ - struct vm_struct *vm; + + /* + * The following three variables can be packed, because + * a vmap_area object is always one of the three states: + * 1) in "free" tree (root is vmap_area_root) + * 2) in "busy" tree (root is free_vmap_area_root) + * 3) in purge list (head is vmap_purge_list) + */ + union { + unsigned long subtree_max_size; /* in "free" tree */ + struct vm_struct *vm; /* in "busy" tree */ + struct llist_node purge_list; /* in purge list */ + }; }; /* -- cgit v1.2.3-71-gd317