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Date: Sat, 4 Jul 2015 21:13:03 +0300
From: Konstantin Khlebnikov <koct9i@...il.com>
To: Gioh Kim <gioh.kim@....com>
Cc: Jeff Layton <jlayton@...chiereds.net>,
Bruce Fields <bfields@...ldses.org>,
Vlastimil Babka <vbabka@...e.cz>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Al Viro <viro@...iv.linux.org.uk>,
"Michael S. Tsirkin" <mst@...hat.com>,
Minchan Kim <minchan@...nel.org>,
Rafael Aquini <aquini@...hat.com>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
virtualization@...ts.linux-foundation.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFCv2 4/5] mm/compaction: compaction calls generic migration
On Fri, Jun 26, 2015 at 12:58 PM, Gioh Kim <gioh.kim@....com> wrote:
> Compaction calls interfaces of driver page migration
> instead of calling balloon migration directly.
>
> Signed-off-by: Gioh Kim <gioh.kim@....com>
> ---
> drivers/virtio/virtio_balloon.c | 1 +
> mm/compaction.c | 9 +++++----
> mm/migrate.c | 21 ++++++++++++---------
> 3 files changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index c49b553..5e5cbea 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -30,6 +30,7 @@
> #include <linux/balloon_compaction.h>
> #include <linux/oom.h>
> #include <linux/wait.h>
> +#include <linux/anon_inodes.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 16e1b57..cc5ec81 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -14,7 +14,7 @@
> #include <linux/backing-dev.h>
> #include <linux/sysctl.h>
> #include <linux/sysfs.h>
> -#include <linux/balloon_compaction.h>
> +#include <linux/compaction.h>
> #include <linux/page-isolation.h>
> #include <linux/kasan.h>
> #include "internal.h"
> @@ -714,12 +714,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>
> /*
> * Check may be lockless but that's ok as we recheck later.
> - * It's possible to migrate LRU pages and balloon pages
> + * It's possible to migrate LRU pages and driver pages
> * Skip any other type of page
> */
> if (!PageLRU(page)) {
> - if (unlikely(balloon_page_movable(page))) {
> - if (balloon_page_isolate(page)) {
> + if (unlikely(driver_page_migratable(page))) {
> + if (page->mapping->a_ops->isolatepage(page,
> + isolate_mode)) {
Dereferencing page->mapping isn't safe here.
Page could be "truncated" from mapping at any time.
As you can see balloon_page_isolate() calls get_page_unless_zero,
trylock_page and only after that checks balloon_page_movable again.
Existing code already does similar unsafe dereference in
__isolate_lru_page(): page->mapping->a_ops->migratepage
> /* Successfully isolated */
> goto isolate_success;
> }
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 236ee25..a0bc1e4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -35,7 +35,7 @@
> #include <linux/hugetlb.h>
> #include <linux/hugetlb_cgroup.h>
> #include <linux/gfp.h>
> -#include <linux/balloon_compaction.h>
> +#include <linux/compaction.h>
> #include <linux/mmu_notifier.h>
>
> #include <asm/tlbflush.h>
> @@ -76,7 +76,7 @@ int migrate_prep_local(void)
> * from where they were once taken off for compaction/migration.
> *
> * This function shall be used whenever the isolated pageset has been
> - * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
> + * built from lru, driver, hugetlbfs page. See isolate_migratepages_range()
> * and isolate_huge_page().
> */
> void putback_movable_pages(struct list_head *l)
> @@ -92,8 +92,8 @@ void putback_movable_pages(struct list_head *l)
> list_del(&page->lru);
> dec_zone_page_state(page, NR_ISOLATED_ANON +
> page_is_file_cache(page));
> - if (unlikely(isolated_balloon_page(page)))
> - balloon_page_putback(page);
> + if (unlikely(driver_page_migratable(page)))
> + page->mapping->a_ops->putbackpage(page);
> else
> putback_lru_page(page);
> }
> @@ -844,15 +844,18 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> }
> }
>
> - if (unlikely(isolated_balloon_page(page))) {
> + if (unlikely(driver_page_migratable(page))) {
> /*
> - * A ballooned page does not need any special attention from
> + * A driver page does not need any special attention from
> * physical to virtual reverse mapping procedures.
> * Skip any attempt to unmap PTEs or to remap swap cache,
> * in order to avoid burning cycles at rmap level, and perform
> * the page migration right away (proteced by page lock).
> */
> - rc = balloon_page_migrate(newpage, page, mode);
> + rc = page->mapping->a_ops->migratepage(page->mapping,
> + newpage,
> + page,
> + mode);
> goto out_unlock;
> }
>
> @@ -962,8 +965,8 @@ out:
> if (rc != MIGRATEPAGE_SUCCESS && put_new_page) {
> ClearPageSwapBacked(newpage);
> put_new_page(newpage, private);
> - } else if (unlikely(__is_movable_balloon_page(newpage))) {
> - /* drop our reference, page already in the balloon */
> + } else if (unlikely(driver_page_migratable(newpage))) {
> + /* drop our reference */
> put_page(newpage);
> } else
> putback_lru_page(newpage);
> --
> 1.9.1
>
--
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