在 2024/6/19 18:13, Barry Song 写道:
+Mel, the original author of commit 5d0a661d808f
('mm/page_alloc: use only one PCP list..."
On Wed, Jun 19, 2024 at 9:48 PM <yangge1116@xxxxxxx> wrote:
From: yangge <yangge1116@xxxxxxx>
Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
THP-sized allocations") no longer differentiates the migration type
of pages in THP-sized PCP list, it's possible that non-movable
allocation requests may get a CMA page from the list, in some cases,
it's not acceptable.
If a large number of CMA memory are configured in system (for
example, the CMA memory accounts for 50% of the system memory),
starting a virtual machine with device passthrough will get stuck.
During starting the virtual machine, it will call
pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally
if a page is present and in CMA area, pin_user_pages_remote() will
migrate the page from CMA area to non-CMA area because of
FOLL_LONGTERM flag. But if non-movable allocation requests return
CMA memory, migrate_longterm_unpinnable_pages() will migrate a CMA
page to another CMA page, which will fail to pass the check in
check_and_migrate_movable_pages() and cause migration endless.
Call trace:
pin_user_pages_remote
--__gup_longterm_locked // endless loops in this function
----_get_user_pages_locked
----check_and_migrate_movable_pages
------migrate_longterm_unpinnable_pages
--------alloc_migration_target
Please also describe its potential negative impact to cma_alloc().
To fix the problem above, we add one PCP list for THP, which will
not introduce a new cacheline. THP will have 2 PCP lists, one PCP
not introduce a new cacheline for struct per_cpu_pages.
list is used by MOVABLE allocation, and the other PCP list is used
by UNMOVABLE allocation. MOVABLE allocation contains GPF_MOVABLE,
and UNMOVABLE allocation contains GFP_UNMOVABLE and GFP_RECLAIMABLE.
Link: https://lore.kernel.org/all/1717492460-19457-1-git-send-email-yangge1116@xxxxxxx/
no this tag.
Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for THP-sized allocations")
Cc: <stable@xxxxxxxxxxxxxxx> ?
Thanks, I will prepare the next version.
Signed-off-by: yangge <yangge1116@xxxxxxx>
---
include/linux/mmzone.h | 9 ++++-----
mm/page_alloc.c | 9 +++++++--
2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b7546dd..cb7f265 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -656,13 +656,12 @@ enum zone_watermarks {
};
/*
- * One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. One additional list
- * for THP which will usually be GFP_MOVABLE. Even if it is another type,
- * it should not contribute to serious fragmentation causing THP allocation
- * failures.
+ * One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. Two additional lists
+ * are added for THP. One PCP list is used by GPF_MOVABLE, and the other PCP list
+ * is used by GFP_UNMOVABLE and GFP_RECLAIMABLE.
*/
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define NR_PCP_THP 1
+#define NR_PCP_THP 2
#else
#define NR_PCP_THP 0
#endif
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8f416a0..0ecbde3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -504,10 +504,15 @@ static void bad_page(struct page *page, const char *reason)
static inline unsigned int order_to_pindex(int migratetype, int order)
{
+ bool __maybe_unused movable;
+
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (order > PAGE_ALLOC_COSTLY_ORDER) {
VM_BUG_ON(order != HPAGE_PMD_ORDER);
- return NR_LOWORDER_PCP_LISTS;
+
+ movable = migratetype == MIGRATE_MOVABLE;
+
+ return NR_LOWORDER_PCP_LISTS + movable;
}
#else
VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
@@ -521,7 +526,7 @@ static inline int pindex_to_order(unsigned int pindex)
int order = pindex / MIGRATE_PCPTYPES;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- if (pindex == NR_LOWORDER_PCP_LISTS)
+ if (order > PAGE_ALLOC_COSTLY_ORDER)
pindex >= NR_LOWORDER_PCP_LISTS
order = HPAGE_PMD_ORDER;
#else
VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
--
2.7.4
Thanks
Barry
