Am 2022-03-01 um 03:03 schrieb David Hildenbrand:
On 28.02.22 21:34, Alex Sierra wrote:
DEVICE_COHERENT pages introduce a subtle distinction in the way
"normal" pages can be used by various callers throughout the kernel.
They behave like normal pages for purposes of mapping in CPU page
tables, and for COW. But they do not support LRU lists, NUMA
migration or THP. Therefore we split vm_normal_page into two
functions vm_normal_any_page and vm_normal_lru_page. The latter will
only return pages that can be put on an LRU list and that support
NUMA migration and THP.
Why not s/vm_normal_any_page/vm_normal_page/ and avoid code churn?
I don't care much, personally, what names we end up with. I'll wait for
a consensus here.
We also introduced a FOLL_LRU flag that adds the same behaviour to
follow_page and related APIs, to allow callers to specify that they
expect to put pages on an LRU list.
[...]
-#define FOLL_WRITE 0x01 /* check pte is writable */
-#define FOLL_TOUCH 0x02 /* mark page accessed */
-#define FOLL_GET 0x04 /* do get_page on page */
-#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
-#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
-#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
- * and return without waiting upon it */
-#define FOLL_POPULATE 0x40 /* fault in pages (with FOLL_MLOCK) */
-#define FOLL_NOFAULT 0x80 /* do not fault in pages */
-#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
-#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
-#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
-#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
-#define FOLL_MLOCK 0x1000 /* lock present pages */
-#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
-#define FOLL_COW 0x4000 /* internal GUP flag */
-#define FOLL_ANON 0x8000 /* don't do file mappings */
-#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
-#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
-#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
-#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
+#define FOLL_WRITE 0x01 /* check pte is writable */
+#define FOLL_TOUCH 0x02 /* mark page accessed */
+#define FOLL_GET 0x04 /* do get_page on page */
+#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
+#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
+#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
+ * and return without waiting upon it */
+#define FOLL_POPULATE 0x40 /* fault in pages (with FOLL_MLOCK) */
+#define FOLL_NOFAULT 0x80 /* do not fault in pages */
+#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
+#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
+#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
+#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
+#define FOLL_MLOCK 0x1000 /* lock present pages */
+#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
+#define FOLL_COW 0x4000 /* internal GUP flag */
+#define FOLL_ANON 0x8000 /* don't do file mappings */
+#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
+#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
+#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
+#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
+#define FOLL_LRU 0x100000 /* return only LRU (anon or page cache) */
Can we minimize code churn, please?
OK. I guess we could unindent the FOLL_LRU number to avoid changing all
the comments.
if (PageReserved(page))
diff --git a/mm/migrate.c b/mm/migrate.c
index c31d04b46a5e..17d049311b78 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1614,7 +1614,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
goto out;
/* FOLL_DUMP to ignore special (like zero) pages */
- follflags = FOLL_GET | FOLL_DUMP;
+ follflags = FOLL_GET | FOLL_DUMP | FOLL_LRU;
page = follow_page(vma, addr, follflags);
Why wouldn't we want to dump DEVICE_COHERENT pages? This looks wrong.
This function later calls isolate_lru_page, which is something you can't
do with a device page.
Regards,
Felix
