Commit 05c3fa9c authored by Pedro Demarchi Gomes's avatar Pedro Demarchi Gomes Committed by Andrew Morton
Browse files

ksm: replace function unmerge_ksm_pages with break_ksm 

Function unmerge_ksm_pages() is unnecessary since now break_ksm() walks an
address range.  So replace it with break_ksm().

Link: https://lkml.kernel.org/r/20251105184912.186329-4-pedrodemargomes@gmail.com


Signed-off-by: default avatarPedro Demarchi Gomes <pedrodemargomes@gmail.com>
Suggested-by: default avatarDavid Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: default avatarDavid Hildenbrand (Red Hat) <david@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 5d4939fc

mm/ksm.c

+16 −24
Original line number Diff line number Diff line
@@ -665,6 +665,18 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = { 
};



/*

 * Though it's very tempting to unmerge rmap_items from stable tree rather

 * than check every pte of a given vma, the locking doesn't quite work for

 * that - an rmap_item is assigned to the stable tree after inserting ksm

 * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing

 * rmap_items from parent to child at fork time (so as not to waste time

 * if exit comes before the next scan reaches it).

 *

 * Similarly, although we'd like to remove rmap_items (so updating counts

 * and freeing memory) when unmerging an area, it's easier to leave that

 * to the next pass of ksmd - consider, for example, how ksmd might be

 * in cmp_and_merge_page on one of the rmap_items we would be removing.

 *

 * We use break_ksm to break COW on a ksm page by triggering unsharing,

 * such that the ksm page will get replaced by an exclusive anonymous page.

 *
@@ -1071,25 +1083,6 @@ static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list) 
	}

}



/*

 * Though it's very tempting to unmerge rmap_items from stable tree rather

 * than check every pte of a given vma, the locking doesn't quite work for

 * that - an rmap_item is assigned to the stable tree after inserting ksm

 * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing

 * rmap_items from parent to child at fork time (so as not to waste time

 * if exit comes before the next scan reaches it).

 *

 * Similarly, although we'd like to remove rmap_items (so updating counts

 * and freeing memory) when unmerging an area, it's easier to leave that

 * to the next pass of ksmd - consider, for example, how ksmd might be

 * in cmp_and_merge_page on one of the rmap_items we would be removing.

 */

static int unmerge_ksm_pages(struct vm_area_struct *vma,

			     unsigned long start, unsigned long end, bool lock_vma)

{

	return break_ksm(vma, start, end, lock_vma);

}



static inline

struct ksm_stable_node *folio_stable_node(const struct folio *folio)

{
@@ -1227,8 +1220,7 @@ static int unmerge_and_remove_all_rmap_items(void) 
		for_each_vma(vmi, vma) {

			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)

				continue;

			err = unmerge_ksm_pages(vma,

						vma->vm_start, vma->vm_end, false);

			err = break_ksm(vma, vma->vm_start, vma->vm_end, false);

			if (err)

				goto error;

		}
@@ -2855,7 +2847,7 @@ static int __ksm_del_vma(struct vm_area_struct *vma) 
		return 0;



	if (vma->anon_vma) {

		err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true);

		err = break_ksm(vma, vma->vm_start, vma->vm_end, true);

		if (err)

			return err;

	}
@@ -3007,7 +2999,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, 
			return 0;		/* just ignore the advice */



		if (vma->anon_vma) {

			err = unmerge_ksm_pages(vma, start, end, true);

			err = break_ksm(vma, start, end, true);

			if (err)

				return err;

		}
@@ -3389,7 +3381,7 @@ static int ksm_memory_callback(struct notifier_block *self, 
		 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()

		 * and remove_all_stable_nodes() while memory is going offline:

		 * it is unsafe for them to touch the stable tree at this time.

		 * But unmerge_ksm_pages(), rmap lookups and other entry points

		 * But break_ksm(), rmap lookups and other entry points

		 * which do not need the ksm_thread_mutex are all safe.

		 */

		mutex_lock(&ksm_thread_mutex);