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authorAlistair Popple <apopple@nvidia.com>2021-11-10 20:32:40 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-11 09:34:35 -0800
commitab09243aa95a72bac5c71e852773de34116f8d0f (patch)
tree825f51109c310ac95b1bf5278394badbec8fd6dc /mm
parent0ef024621417fa3fcdeb2c3320f90ee34e18a5d9 (diff)
downloadlinux-ab09243aa95a72bac5c71e852773de34116f8d0f.tar.bz2
mm/migrate.c: remove MIGRATE_PFN_LOCKED
MIGRATE_PFN_LOCKED is used to indicate to migrate_vma_prepare() that a source page was already locked during migrate_vma_collect(). If it wasn't then the a second attempt is made to lock the page. However if the first attempt failed it's unlikely a second attempt will succeed, and the retry adds complexity. So clean this up by removing the retry and MIGRATE_PFN_LOCKED flag. Destination pages are also meant to have the MIGRATE_PFN_LOCKED flag set, but nothing actually checks that. Link: https://lkml.kernel.org/r/20211025041608.289017-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ralph Campbell <rcampbell@nvidia.com> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Zi Yan <ziy@nvidia.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Ben Skeggs <bskeggs@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/migrate.c145
1 files changed, 28 insertions, 117 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 43dd88c7fcdc..cf25b00f03c8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2362,7 +2362,6 @@ again:
* can't be dropped from it).
*/
get_page(page);
- migrate->cpages++;
/*
* Optimize for the common case where page is only mapped once
@@ -2372,7 +2371,7 @@ again:
if (trylock_page(page)) {
pte_t swp_pte;
- mpfn |= MIGRATE_PFN_LOCKED;
+ migrate->cpages++;
ptep_get_and_clear(mm, addr, ptep);
/* Setup special migration page table entry */
@@ -2406,6 +2405,9 @@ again:
if (pte_present(pte))
unmapped++;
+ } else {
+ put_page(page);
+ mpfn = 0;
}
next:
@@ -2510,15 +2512,17 @@ static bool migrate_vma_check_page(struct page *page)
}
/*
- * migrate_vma_prepare() - lock pages and isolate them from the lru
+ * migrate_vma_unmap() - replace page mapping with special migration pte entry
* @migrate: migrate struct containing all migration information
*
- * This locks pages that have been collected by migrate_vma_collect(). Once each
- * page is locked it is isolated from the lru (for non-device pages). Finally,
- * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be
- * migrated by concurrent kernel threads.
+ * Isolate pages from the LRU and replace mappings (CPU page table pte) with a
+ * special migration pte entry and check if it has been pinned. Pinned pages are
+ * restored because we cannot migrate them.
+ *
+ * This is the last step before we call the device driver callback to allocate
+ * destination memory and copy contents of original page over to new page.
*/
-static void migrate_vma_prepare(struct migrate_vma *migrate)
+static void migrate_vma_unmap(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
const unsigned long start = migrate->start;
@@ -2527,32 +2531,12 @@ static void migrate_vma_prepare(struct migrate_vma *migrate)
lru_add_drain();
- for (i = 0; (i < npages) && migrate->cpages; i++) {
+ for (i = 0; i < npages; i++) {
struct page *page = migrate_pfn_to_page(migrate->src[i]);
- bool remap = true;
if (!page)
continue;
- if (!(migrate->src[i] & MIGRATE_PFN_LOCKED)) {
- /*
- * Because we are migrating several pages there can be
- * a deadlock between 2 concurrent migration where each
- * are waiting on each other page lock.
- *
- * Make migrate_vma() a best effort thing and backoff
- * for any page we can not lock right away.
- */
- if (!trylock_page(page)) {
- migrate->src[i] = 0;
- migrate->cpages--;
- put_page(page);
- continue;
- }
- remap = false;
- migrate->src[i] |= MIGRATE_PFN_LOCKED;
- }
-
/* ZONE_DEVICE pages are not on LRU */
if (!is_zone_device_page(page)) {
if (!PageLRU(page) && allow_drain) {
@@ -2562,16 +2546,9 @@ static void migrate_vma_prepare(struct migrate_vma *migrate)
}
if (isolate_lru_page(page)) {
- if (remap) {
- migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
- migrate->cpages--;
- restore++;
- } else {
- migrate->src[i] = 0;
- unlock_page(page);
- migrate->cpages--;
- put_page(page);
- }
+ migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+ migrate->cpages--;
+ restore++;
continue;
}
@@ -2579,80 +2556,20 @@ static void migrate_vma_prepare(struct migrate_vma *migrate)
put_page(page);
}
- if (!migrate_vma_check_page(page)) {
- if (remap) {
- migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
- migrate->cpages--;
- restore++;
-
- if (!is_zone_device_page(page)) {
- get_page(page);
- putback_lru_page(page);
- }
- } else {
- migrate->src[i] = 0;
- unlock_page(page);
- migrate->cpages--;
+ if (page_mapped(page))
+ try_to_migrate(page, 0);
- if (!is_zone_device_page(page))
- putback_lru_page(page);
- else
- put_page(page);
+ if (page_mapped(page) || !migrate_vma_check_page(page)) {
+ if (!is_zone_device_page(page)) {
+ get_page(page);
+ putback_lru_page(page);
}
- }
- }
-
- for (i = 0, addr = start; i < npages && restore; i++, addr += PAGE_SIZE) {
- struct page *page = migrate_pfn_to_page(migrate->src[i]);
-
- if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
- continue;
- remove_migration_pte(page, migrate->vma, addr, page);
-
- migrate->src[i] = 0;
- unlock_page(page);
- put_page(page);
- restore--;
- }
-}
-
-/*
- * migrate_vma_unmap() - replace page mapping with special migration pte entry
- * @migrate: migrate struct containing all migration information
- *
- * Replace page mapping (CPU page table pte) with a special migration pte entry
- * and check again if it has been pinned. Pinned pages are restored because we
- * cannot migrate them.
- *
- * This is the last step before we call the device driver callback to allocate
- * destination memory and copy contents of original page over to new page.
- */
-static void migrate_vma_unmap(struct migrate_vma *migrate)
-{
- const unsigned long npages = migrate->npages;
- const unsigned long start = migrate->start;
- unsigned long addr, i, restore = 0;
-
- for (i = 0; i < npages; i++) {
- struct page *page = migrate_pfn_to_page(migrate->src[i]);
-
- if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE))
+ migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+ migrate->cpages--;
+ restore++;
continue;
-
- if (page_mapped(page)) {
- try_to_migrate(page, 0);
- if (page_mapped(page))
- goto restore;
}
-
- if (migrate_vma_check_page(page))
- continue;
-
-restore:
- migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
- migrate->cpages--;
- restore++;
}
for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) {
@@ -2665,12 +2582,8 @@ restore:
migrate->src[i] = 0;
unlock_page(page);
+ put_page(page);
restore--;
-
- if (is_zone_device_page(page))
- put_page(page);
- else
- putback_lru_page(page);
}
}
@@ -2693,8 +2606,8 @@ restore:
* it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
* flag set). Once these are allocated and copied, the caller must update each
* corresponding entry in the dst array with the pfn value of the destination
- * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_LOCKED flags set
- * (destination pages must have their struct pages locked, via lock_page()).
+ * page and with MIGRATE_PFN_VALID. Destination pages must be locked via
+ * lock_page().
*
* Note that the caller does not have to migrate all the pages that are marked
* with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
@@ -2764,8 +2677,6 @@ int migrate_vma_setup(struct migrate_vma *args)
migrate_vma_collect(args);
if (args->cpages)
- migrate_vma_prepare(args);
- if (args->cpages)
migrate_vma_unmap(args);
/*