From 505ecd7b30fca1dc296205ff3c0dc3aff9d76e12 Mon Sep 17 00:00:00 2001 From: Sergey Bugaev Date: Mon, 26 Jun 2023 14:26:50 +0300 Subject: Shrink struct vm_page size struct vm_page is supposed to be a "small structure", but it takes up 96 bytes on x86_64 (to represent a 4k page). By utilizing bitfields and strategically reordering members to avoid excessive padding, it can be shrunk to 80 bytes. - page_lock and unlock_request only need to store a bitmask of VM_PROT_READ, VM_PROT_WRITE, and VM_PROT_EXECUTE. Even though the special values VM_PROT_NO_CHANGE and VM_PROT_NOTIFY are defined, they are not used for the two struct vm_page members. - type and seg_index both need to store one of the four possible values in the range from 0 to 3. Two bits are sufficient for this. - order needs to store a number from 0 to VM_PAGE_NR_FREE_LISTS (which is 11), or a special value VM_PAGE_ORDER_UNLISTED. Four bits are sufficient for this. No functional change. Message-Id: <20230626112656.435622-2-bugaevc@gmail.com> --- vm/vm_resident.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'vm/vm_resident.c') diff --git a/vm/vm_resident.c b/vm/vm_resident.c index e0a03bf5..d4777e70 100644 --- a/vm/vm_resident.c +++ b/vm/vm_resident.c @@ -746,7 +746,7 @@ boolean_t vm_page_convert(struct vm_page **mp) memcpy(&real_m->vm_page_header, &fict_m->vm_page_header, - sizeof(*fict_m) - VM_PAGE_HEADER_SIZE); + VM_PAGE_BODY_SIZE); real_m->fictitious = FALSE; vm_page_insert(real_m, object, offset); -- cgit v1.2.3