From 304dbdb7a4fbb7f40a6ad5c5836fdd456c233c63 Mon Sep 17 00:00:00 2001 From: Lee Schermerhorn Date: Sat, 22 Apr 2006 02:35:48 -0700 Subject: [PATCH] [PATCH] add migratepage address space op to shmem Basic problem: pages of a shared memory segment can only be migrated once. In 2.6.16 through 2.6.17-rc1, shared memory mappings do not have a migratepage address space op. Therefore, migrate_pages() falls back to default processing. In this path, it will try to pageout() dirty pages. Once a shared memory page has been migrated it becomes dirty, so migrate_pages() will try to page it out. However, because the page count is 3 [cache + current + pte], pageout() will return PAGE_KEEP because is_page_cache_freeable() returns false. This will abort all subsequent migrations. This patch adds a migratepage address space op to shared memory segments to avoid taking the default path. We use the "migrate_page()" function because it knows how to migrate dirty pages. This allows shared memory segment pages to migrate, subject to other conditions such as # pte's referencing the page [page_mapcount(page)], when requested. I think this is safe. If we're migrating a shared memory page, then we found the page via a page table, so it must be in memory. Can be verified with memtoy and the shmem-mbind-test script, both available at: http://free.linux.hp.com/~lts/Tools/ Signed-off-by: Lee Schermerhorn Acked-by: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/shmem.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 37eaf42ed2c..4c5e68e4e9a 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -46,6 +46,8 @@ #include #include #include +#include + #include #include #include @@ -2173,6 +2175,7 @@ static struct address_space_operations shmem_aops = { .prepare_write = shmem_prepare_write, .commit_write = simple_commit_write, #endif + .migratepage = migrate_page, }; static struct file_operations shmem_file_operations = { -- 2.20.1