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Date: Sat, 4 Jul 2015 22:00:26 +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 Sat, Jul 4, 2015 at 9:13 PM, Konstantin Khlebnikov <koct9i@...il.com> wrote:
> 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.
Page must be getted and locked before calling aops method, somethin like this:
If (!PageLRU(page)) {
if (PageBalloon(page) || PageMobile(page))
if (get_page_unless_zero(page))
if (try_lock(page))
if (page->mapping && page->mapping->a_ops->isolatepage)
page->mapping->a_ops->isolate_page(page, ...)
....
>
> 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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