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Date: Wed, 17 Jul 2013 13:22:22 +0800
From: Sam Ben <sam.bennn@...il.com>
To: Mel Gorman <mgorman@...e.de>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Linux-MM <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount
On 07/15/2013 11:20 PM, Mel Gorman wrote:
> Currently automatic NUMA balancing is unable to distinguish between false
> shared versus private pages except by ignoring pages with an elevated
What's the meaning of false shared?
> page_mapcount entirely. This avoids shared pages bouncing between the
> nodes whose task is using them but that is ignored quite a lot of data.
>
> This patch kicks away the training wheels in preparation for adding support
> for identifying shared/private pages is now in place. The ordering is so
> that the impact of the shared/private detection can be easily measured. Note
> that the patch does not migrate shared, file-backed within vmas marked
> VM_EXEC as these are generally shared library pages. Migrating such pages
> is not beneficial as there is an expectation they are read-shared between
> caches and iTLB and iCache pressure is generally low.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
> include/linux/migrate.h | 7 ++++---
> mm/memory.c | 7 ++-----
> mm/migrate.c | 17 ++++++-----------
> mm/mprotect.c | 4 +---
> 4 files changed, 13 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index a405d3dc..e7e26af 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -92,11 +92,12 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
> #endif /* CONFIG_MIGRATION */
>
> #ifdef CONFIG_NUMA_BALANCING
> -extern int migrate_misplaced_page(struct page *page, int node);
> -extern int migrate_misplaced_page(struct page *page, int node);
> +extern int migrate_misplaced_page(struct page *page,
> + struct vm_area_struct *vma, int node);
> extern bool migrate_ratelimited(int node);
> #else
> -static inline int migrate_misplaced_page(struct page *page, int node)
> +static inline int migrate_misplaced_page(struct page *page,
> + struct vm_area_struct *vma, int node)
> {
> return -EAGAIN; /* can't migrate now */
> }
> diff --git a/mm/memory.c b/mm/memory.c
> index ab933be..62ae8a7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3586,7 +3586,7 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
> }
>
> /* Migrate to the requested node */
> - migrated = migrate_misplaced_page(page, target_nid);
> + migrated = migrate_misplaced_page(page, vma, target_nid);
> if (migrated)
> current_nid = target_nid;
>
> @@ -3651,9 +3651,6 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
> page = vm_normal_page(vma, addr, pteval);
> if (unlikely(!page))
> continue;
> - /* only check non-shared pages */
> - if (unlikely(page_mapcount(page) != 1))
> - continue;
>
> /*
> * Note that the NUMA fault is later accounted to either
> @@ -3671,7 +3668,7 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
>
> /* Migrate to the requested node */
> pte_unmap_unlock(pte, ptl);
> - migrated = migrate_misplaced_page(page, target_nid);
> + migrated = migrate_misplaced_page(page, vma, target_nid);
> if (migrated)
> curr_nid = target_nid;
> task_numa_fault(last_nid, curr_nid, 1, migrated);
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 3bbaf5d..23f8122 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1579,7 +1579,8 @@ int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> * node. Caller is expected to have an elevated reference count on
> * the page that will be dropped by this function before returning.
> */
> -int migrate_misplaced_page(struct page *page, int node)
> +int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
> + int node)
> {
> pg_data_t *pgdat = NODE_DATA(node);
> int isolated;
> @@ -1587,10 +1588,11 @@ int migrate_misplaced_page(struct page *page, int node)
> LIST_HEAD(migratepages);
>
> /*
> - * Don't migrate pages that are mapped in multiple processes.
> - * TODO: Handle false sharing detection instead of this hammer
> + * Don't migrate file pages that are mapped in multiple processes
> + * with execute permissions as they are probably shared libraries.
> */
> - if (page_mapcount(page) != 1)
> + if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
> + (vma->vm_flags & VM_EXEC))
> goto out;
>
> /*
> @@ -1641,13 +1643,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> int page_lru = page_is_file_cache(page);
>
> /*
> - * Don't migrate pages that are mapped in multiple processes.
> - * TODO: Handle false sharing detection instead of this hammer
> - */
> - if (page_mapcount(page) != 1)
> - goto out_dropref;
> -
> - /*
> * Rate-limit the amount of data that is being migrated to a node.
> * Optimal placement is no good if the memory bus is saturated and
> * all the time is being spent migrating!
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 94722a4..cacc64a 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -69,9 +69,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> if (last_nid != this_nid)
> all_same_node = false;
>
> - /* only check non-shared pages */
> - if (!pte_numa(oldpte) &&
> - page_mapcount(page) == 1) {
> + if (!pte_numa(oldpte)) {
> ptent = pte_mknuma(ptent);
> updated = true;
> }
--
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