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Commit 6514d511 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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ksm: singly-linked rmap_list 



Free up a pointer in struct rmap_item, by making the mm_slot's rmap_list a
singly-linked list: we always traverse that list sequentially, and we
don't even lose any prefetches (but should consider adding a few later).
Name it rmap_list throughout.

Do we need to free up that pointer?  Not immediately, and in the end, we
could continue to avoid it with a union; but having done the conversion,
let's keep it this way, since there's no downside, and maybe we'll want
more in future (struct rmap_item is a cache-friendly 32 bytes on 32-bit
and 64 bytes on 64-bit, so we shall want to avoid expanding it).

Signed-off-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8dd3557a

mm/ksm.c

+26 −30
Original line number Diff line number Diff line
@@ -79,13 +79,13 @@ 
 * struct mm_slot - ksm information per mm that is being scanned

 * @link: link to the mm_slots hash list

 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head

 * @rmap_list: head for this mm_slot's list of rmap_items

 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items

 * @mm: the mm that this information is valid for

 */

struct mm_slot {

	struct hlist_node link;

	struct list_head mm_list;

	struct list_head rmap_list;

	struct rmap_item *rmap_list;

	struct mm_struct *mm;

};
@@ -93,7 +93,7 @@ struct mm_slot { 
 * struct ksm_scan - cursor for scanning

 * @mm_slot: the current mm_slot we are scanning

 * @address: the next address inside that to be scanned

 * @rmap_item: the current rmap that we are scanning inside the rmap_list

 * @rmap_list: link to the next rmap to be scanned in the rmap_list

 * @seqnr: count of completed full scans (needed when removing unstable node)

 *

 * There is only the one ksm_scan instance of this cursor structure.
@@ -101,13 +101,14 @@ struct mm_slot { 
struct ksm_scan {

	struct mm_slot *mm_slot;

	unsigned long address;

	struct rmap_item *rmap_item;

	struct rmap_item **rmap_list;

	unsigned long seqnr;

};



/**

 * struct rmap_item - reverse mapping item for virtual addresses

 * @link: link into mm_slot's rmap_list (rmap_list is per mm)

 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list

 * @filler: unused space we're making available in this patch

 * @mm: the memory structure this rmap_item is pointing into

 * @address: the virtual address this rmap_item tracks (+ flags in low bits)

 * @oldchecksum: previous checksum of the page at that virtual address
@@ -116,7 +117,8 @@ struct ksm_scan { 
 * @prev: previous rmap_item hanging off the same node of the stable tree

 */

struct rmap_item {

	struct list_head link;

	struct rmap_item *rmap_list;

	unsigned long filler;

	struct mm_struct *mm;

	unsigned long address;		/* + low bits used for flags below */

	union {
@@ -275,7 +277,6 @@ static void insert_to_mm_slots_hash(struct mm_struct *mm, 
	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))

				% MM_SLOTS_HASH_HEADS];

	mm_slot->mm = mm;

	INIT_LIST_HEAD(&mm_slot->rmap_list);

	hlist_add_head(&mm_slot->link, bucket);

}
@@ -479,15 +480,12 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) 
}



static void remove_trailing_rmap_items(struct mm_slot *mm_slot,

				       struct list_head *cur)

				       struct rmap_item **rmap_list)

{

	struct rmap_item *rmap_item;



	while (cur != &mm_slot->rmap_list) {

		rmap_item = list_entry(cur, struct rmap_item, link);

		cur = cur->next;

	while (*rmap_list) {

		struct rmap_item *rmap_item = *rmap_list;

		*rmap_list = rmap_item->rmap_list;

		remove_rmap_item_from_tree(rmap_item);

		list_del(&rmap_item->link);

		free_rmap_item(rmap_item);

	}

}
@@ -553,7 +551,7 @@ static int unmerge_and_remove_all_rmap_items(void) 
				goto error;

		}



		remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);

		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);



		spin_lock(&ksm_mmlist_lock);

		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
@@ -1141,20 +1139,19 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) 
}



static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,

					    struct list_head *cur,

					    struct rmap_item **rmap_list,

					    unsigned long addr)

{

	struct rmap_item *rmap_item;



	while (cur != &mm_slot->rmap_list) {

		rmap_item = list_entry(cur, struct rmap_item, link);

	while (*rmap_list) {

		rmap_item = *rmap_list;

		if ((rmap_item->address & PAGE_MASK) == addr)

			return rmap_item;

		if (rmap_item->address > addr)

			break;

		cur = cur->next;

		*rmap_list = rmap_item->rmap_list;

		remove_rmap_item_from_tree(rmap_item);

		list_del(&rmap_item->link);

		free_rmap_item(rmap_item);

	}
@@ -1163,7 +1160,8 @@ static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, 
		/* It has already been zeroed */

		rmap_item->mm = mm_slot->mm;

		rmap_item->address = addr;

		list_add_tail(&rmap_item->link, cur);

		rmap_item->rmap_list = *rmap_list;

		*rmap_list = rmap_item;

	}

	return rmap_item;

}
@@ -1188,8 +1186,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) 
		spin_unlock(&ksm_mmlist_lock);

next_mm:

		ksm_scan.address = 0;

		ksm_scan.rmap_item = list_entry(&slot->rmap_list,

						struct rmap_item, link);

		ksm_scan.rmap_list = &slot->rmap_list;

	}



	mm = slot->mm;
@@ -1215,10 +1212,10 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) 
				flush_anon_page(vma, *page, ksm_scan.address);

				flush_dcache_page(*page);

				rmap_item = get_next_rmap_item(slot,

					ksm_scan.rmap_item->link.next,

					ksm_scan.address);

					ksm_scan.rmap_list, ksm_scan.address);

				if (rmap_item) {

					ksm_scan.rmap_item = rmap_item;

					ksm_scan.rmap_list =

							&rmap_item->rmap_list;

					ksm_scan.address += PAGE_SIZE;

				} else

					put_page(*page);
@@ -1234,14 +1231,13 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) 


	if (ksm_test_exit(mm)) {

		ksm_scan.address = 0;

		ksm_scan.rmap_item = list_entry(&slot->rmap_list,

						struct rmap_item, link);

		ksm_scan.rmap_list = &slot->rmap_list;

	}

	/*

	 * Nuke all the rmap_items that are above this current rmap:

	 * because there were no VM_MERGEABLE vmas with such addresses.

	 */

	remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);

	remove_trailing_rmap_items(slot, ksm_scan.rmap_list);



	spin_lock(&ksm_mmlist_lock);

	ksm_scan.mm_slot = list_entry(slot->mm_list.next,
@@ -1423,7 +1419,7 @@ void __ksm_exit(struct mm_struct *mm) 
	spin_lock(&ksm_mmlist_lock);

	mm_slot = get_mm_slot(mm);

	if (mm_slot && ksm_scan.mm_slot != mm_slot) {

		if (list_empty(&mm_slot->rmap_list)) {

		if (!mm_slot->rmap_list) {

			hlist_del(&mm_slot->link);

			list_del(&mm_slot->mm_list);

			easy_to_free = 1;