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Message-ID: <20150731104309.GA22158@bbox>
Date: Fri, 31 Jul 2015 19:43:09 +0900
From: Minchan Kim <minchan@...nel.org>
To: Gioh Kim <gioh.kim@....com>
Cc: jlayton@...chiereds.net, bfields@...ldses.org, vbabka@...e.cz,
iamjoonsoo.kim@....com, viro@...iv.linux.org.uk, mst@...hat.com,
koct9i@...il.com, aquini@...hat.com, linux-fsdevel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
linux-mm@...ck.org, dri-devel@...ts.freedesktop.org,
akpm@...ux-foundation.org, Gioh Kim <gurugio@...mail.net>
Subject: Re: [PATCH 2/4] mm/compaction: enable mobile-page migration
Hi Gioh,
On Mon, Jul 13, 2015 at 05:35:17PM +0900, Gioh Kim wrote:
> From: Gioh Kim <gurugio@...mail.net>
>
> 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 <gioh.kim@....com>
> Acked-by: Rafael Aquini <aquini@...hat.com>
> ---
> fs/proc/page.c | 3 ++
> include/linux/compaction.h | 80 ++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 +
> include/linux/page-flags.h | 19 ++++++++
> include/uapi/linux/kernel-page-flags.h | 1 +
> 5 files changed, 105 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;
> +
Need a new page flag for non-LRU page migration?
I am worry that we don't have empty slot for page flag on 32-bit.
Aha, see SetPageMobile below. You use _mapcount.
It seems to be work for non-LRU pages but unfortunately, zsmalloc
already have used that field as own purpose so there is no room
for it.
> 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..f693072 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 +54,70 @@ 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 && (PageMobile(page) || PageBalloon(page));
What's the locking rule to test mobile_page?
Why we need such many checking?
Why we need PageBalloon check?
You are trying to make generic abstraction for non-LRU page to migrate
but PageBalloon check in here breaks your goal.
> +}
> +
> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
> +{
> + bool ret = false;
> +
> + /*
> + * 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.
> + */
Good.
> + if (unlikely(!get_page_unless_zero(page)))
> + goto out;
> +
> + /*
> + * 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.
How can it race with releasing a page?
We already get refcount above.
Do you mean page->mapping tearing race?
If so, zsmalloc should be chaned to hold a lock.
> + *
> + * 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 (unlikely(!trylock_page(page)))
> + goto out_putpage;
> +
> + if (!(mobile_page(page) && page->mapping->a_ops->isolatepage))
> + goto out_not_isolated;
I cannot know how isolate_mobilepage is called by upper layer
because this patch doesn't include it.
Anyway, why we need such many checks to prove it's mobile page?
mobile_page() {
page->mapping && (PageMobile(page) || PageBalloon(page));
}
Additionally, added page->mapping->a_ops->isolatepage check
Is it possible that a non-LRU page's address space provides
only page->maping->migratepage without isolate/putback?
Couldn't we make it simple like this?
page->mapping && page->mapping->migratepage
So, couldn't we make mobile_page like this
PageMobile(struct page *page)
{
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageLRU(page), page);
return page->mapping && page->mapping->migratepage;
}
It will save _mapcount of struct page.
> + ret = page->mapping->a_ops->isolatepage(page, mode);
> + if (!ret)
> + goto out_not_isolated;
> + unlock_page(page);
> + return ret;
> +
> +out_not_isolated:
> + unlock_page(page);
> +out_putpage:
> + put_page(page);
> +out:
> + return ret;
> +}
> +
> +static inline void putback_mobilepage(struct page *page)
> +{
> + /*
> + * 'lock_page()' stabilizes the page and prevents races against
What does it mean 'stabilize'?
Clear comment is always welcome rather than vague word.
> + * concurrent isolation threads attempting to re-isolate it.
> + */
> + lock_page(page);
> + if (page->mapping && page->mapping->a_ops->putbackpage)
> + page->mapping->a_ops->putbackpage(page);
> + unlock_page(page);
> + /* drop the extra ref count taken for mobile page isolation */
> + put_page(page);
> +}
> #else
> static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
> unsigned int order, int alloc_flags,
> @@ -83,6 +150,19 @@ 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 a0653e5..2cc4b24 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -396,6 +396,8 @@ 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
>
--
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