by Konstantin Khlebnikov

[permalink] [raw]

Subject: Re: [RFCv3 2/5] mm/compaction: enable mobile-page migration

One more note below.

On Tue, Jul 7, 2015 at 7:36 AM, Gioh Kim <[email protected]> wrote:
> From: Gioh Kim <[email protected]>
>
> Add framework to register callback functions and check page mobility.
> There are some modes for page isolation so that isolate interface
> has arguments of page address and isolation mode while putback
> interface has only page address as argument.
>
> Signed-off-by: Gioh Kim <[email protected]>
> ---
> fs/proc/page.c | 3 ++
> include/linux/compaction.h | 76 ++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 +
> include/linux/page-flags.h | 19 +++++++++
> include/uapi/linux/kernel-page-flags.h | 1 +
> 5 files changed, 101 insertions(+)
>
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 7eee2d8..a4f5a00 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -146,6 +146,9 @@ u64 stable_page_flags(struct page *page)
> if (PageBalloon(page))
> u |= 1 << KPF_BALLOON;
>
> + if (PageMobile(page))
> + u |= 1 << KPF_MOBILE;
> +
> u |= kpf_copy_bit(k, KPF_LOCKED, PG_locked);
>
> u |= kpf_copy_bit(k, KPF_SLAB, PG_slab);
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index aa8f61c..c375a89 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -1,6 +1,9 @@
> #ifndef _LINUX_COMPACTION_H
> #define _LINUX_COMPACTION_H
>
> +#include <linux/page-flags.h>
> +#include <linux/pagemap.h>
> +
> /* Return values for compact_zone() and try_to_compact_pages() */
> /* compaction didn't start as it was deferred due to past failures */
> #define COMPACT_DEFERRED 0
> @@ -51,6 +54,66 @@ extern void compaction_defer_reset(struct zone *zone, int order,
> bool alloc_success);
> extern bool compaction_restarting(struct zone *zone, int order);
>
> +static inline bool mobile_page(struct page *page)
> +{
> + return page->mapping && page->mapping->a_ops &&
> + (PageMobile(page) || PageBalloon(page));
> +}
> +
> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
> +{
> + bool ret;
> +
> + /*
> + * Avoid burning cycles with pages that are yet under __free_pages(),
> + * or just got freed under us.
> + *
> + * In case we 'win' a race for a mobile page being freed under us and
> + * raise its refcount preventing __free_pages() from doing its job
> + * the put_page() at the end of this block will take care of
> + * release this page, thus avoiding a nasty leakage.
> + */
> + if (likely(get_page_unless_zero(page))) {
> + /*
> + * As mobile pages are not isolated from LRU lists, concurrent
> + * compaction threads can race against page migration functions
> + * as well as race against the releasing a page.
> + *
> + * In order to avoid having an already isolated mobile page
> + * being (wrongly) re-isolated while it is under migration,
> + * or to avoid attempting to isolate pages being released,
> + * lets be sure we have the page lock
> + * before proceeding with the mobile page isolation steps.
> + */
> + if (likely(trylock_page(page))) {
> + if (mobile_page(page) &&
> + page->mapping->a_ops->isolatepage) {
> + ret = page->mapping->a_ops->isolatepage(page,
> + mode);
> + unlock_page(page);

Here you leak page reference if isolatepage() fails.

> + return ret;
> + }
> + unlock_page(page);
> + }
> + put_page(page);
> + }
> + return false;
> +}
> +
> +static inline void putback_mobilepage(struct page *page)
> +{
> + /*
> + * 'lock_page()' stabilizes the page and prevents races against
> + * concurrent isolation threads attempting to re-isolate it.
> + */
> + lock_page(page);
> + if (mobile_page(page) && page->mapping->a_ops->putbackpage) {
> + page->mapping->a_ops->putbackpage(page);
> + /* drop the extra ref count taken for mobile page isolation */
> + put_page(page);
> + }
> + unlock_page(page);
> +}
> #else
> static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
> unsigned int order, int alloc_flags,
> @@ -83,6 +146,19 @@ static inline bool compaction_deferred(struct zone *zone, int order)
> return true;
> }
>
> +static inline bool mobile_page(struct page *page)
> +{
> + return false;
> +}
> +
> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
> +{
> + return false;
> +}
> +
> +static inline void putback_mobilepage(struct page *page)
> +{
> +}
> #endif /* CONFIG_COMPACTION */
>
> #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 35ec87e..33c9aa5 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -395,6 +395,8 @@ struct address_space_operations {
> */
> int (*migratepage) (struct address_space *,
> struct page *, struct page *, enum migrate_mode);
> + bool (*isolatepage) (struct page *, isolate_mode_t);
> + void (*putbackpage) (struct page *);
> int (*launder_page) (struct page *);
> int (*is_partially_uptodate) (struct page *, unsigned long,
> unsigned long);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index f34e040..abef145 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -582,6 +582,25 @@ static inline void __ClearPageBalloon(struct page *page)
> atomic_set(&page->_mapcount, -1);
> }
>
> +#define PAGE_MOBILE_MAPCOUNT_VALUE (-255)
> +
> +static inline int PageMobile(struct page *page)
> +{
> + return atomic_read(&page->_mapcount) == PAGE_MOBILE_MAPCOUNT_VALUE;
> +}
> +
> +static inline void __SetPageMobile(struct page *page)
> +{
> + VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
> + atomic_set(&page->_mapcount, PAGE_MOBILE_MAPCOUNT_VALUE);
> +}
> +
> +static inline void __ClearPageMobile(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageMobile(page), page);
> + atomic_set(&page->_mapcount, -1);
> +}
> +
> /*
> * If network-based swap is enabled, sl*b must keep track of whether pages
> * were allocated from pfmemalloc reserves.
> diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
> index a6c4962..d50d9e8 100644
> --- a/include/uapi/linux/kernel-page-flags.h
> +++ b/include/uapi/linux/kernel-page-flags.h
> @@ -33,6 +33,7 @@
> #define KPF_THP 22
> #define KPF_BALLOON 23
> #define KPF_ZERO_PAGE 24
> +#define KPF_MOBILE 25
>
>
> #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
> --
> 2.1.4
>

2015-07-13 08:45:50

by Gioh Kim

[permalink] [raw]

Subject: Re: [RFCv3 2/5] mm/compaction: enable mobile-page migration

>> @@ -51,6 +54,66 @@ extern void compaction_defer_reset(struct zone *zone, int order,
>> bool alloc_success);
>> extern bool compaction_restarting(struct zone *zone, int order);
>>
>> +static inline bool mobile_page(struct page *page)
>> +{
>> + return page->mapping && page->mapping->a_ops &&
>
> Dereferncing mapping->a_ops isn't safe without page-lock and isn't required:
> all mappings always have ->a_ops.
>

I got it.

>> +static inline void putback_mobilepage(struct page *page)
>> +{
>> + /*
>> + * 'lock_page()' stabilizes the page and prevents races against
>> + * concurrent isolation threads attempting to re-isolate it.
>> + */
>> + lock_page(page);
>> + if (mobile_page(page) && page->mapping->a_ops->putbackpage) {
>
> It seems "if (page->mapping && page->mapping->a_ops->putbackpage)"
> should be enough: we already seen that page as mobile.

Ditto.

>
>> + page->mapping->a_ops->putbackpage(page);
>> + /* drop the extra ref count taken for mobile page isolation */
>> + put_page(page);
>> + }
>> + unlock_page(page);
>
> call put_page() after unlock and do that always -- putback must drop
> page reference from caller.
>
> lock_page(page);
> if (page->mapping && page->mapping->a_ops->putbackpage)
> page->mapping->a_ops->putbackpage(page);
> unlock_page();
> put_page(page);
>

Ditto.

>> +}
>> #else
>> static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
>> unsigned int order, int alloc_flags,
>> @@ -83,6 +146,19 @@ static inline bool compaction_deferred(struct zone *zone, int order)
>> return true;
>> }
>>
>> +static inline bool mobile_page(struct page *page)
>> +{
>> + return false;
>> +}
>> +
>> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
>> +{
>> + return false;
>> +}
>> +
>> +static inline void putback_mobilepage(struct page *page)
>> +{
>> +}
>> #endif /* CONFIG_COMPACTION */
>>
>> #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 35ec87e..33c9aa5 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -395,6 +395,8 @@ struct address_space_operations {
>> */
>> int (*migratepage) (struct address_space *,
>> struct page *, struct page *, enum migrate_mode);
>> + bool (*isolatepage) (struct page *, isolate_mode_t);
>> + void (*putbackpage) (struct page *);
>> int (*launder_page) (struct page *);
>> int (*is_partially_uptodate) (struct page *, unsigned long,
>> unsigned long);
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index f34e040..abef145 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -582,6 +582,25 @@ static inline void __ClearPageBalloon(struct page *page)
>> atomic_set(&page->_mapcount, -1);
>> }
>>
>> +#define PAGE_MOBILE_MAPCOUNT_VALUE (-255)
>> +
>> +static inline int PageMobile(struct page *page)
>> +{
>> + return atomic_read(&page->_mapcount) == PAGE_MOBILE_MAPCOUNT_VALUE;
>> +}
>> +
>> +static inline void __SetPageMobile(struct page *page)
>> +{
>> + VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
>> + atomic_set(&page->_mapcount, PAGE_MOBILE_MAPCOUNT_VALUE);
>> +}
>> +
>> +static inline void __ClearPageMobile(struct page *page)
>> +{
>> + VM_BUG_ON_PAGE(!PageMobile(page), page);
>> + atomic_set(&page->_mapcount, -1);
>> +}
>> +
>> /*
>> * If network-based swap is enabled, sl*b must keep track of whether pages
>> * were allocated from pfmemalloc reserves.
>> diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
>> index a6c4962..d50d9e8 100644
>> --- a/include/uapi/linux/kernel-page-flags.h
>> +++ b/include/uapi/linux/kernel-page-flags.h
>> @@ -33,6 +33,7 @@
>> #define KPF_THP 22
>> #define KPF_BALLOON 23
>> #define KPF_ZERO_PAGE 24
>> +#define KPF_MOBILE 25
>>
>>
>> #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
>> --
>> 2.1.4
>>
>

I fixed the code as your comments and I found patch 3/5 and 4/5 could not be applied separately.
So I merge them and report new [PATCH].
I appreciate your reviews.