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Date: Tue, 3 Sep 2013 14:56:42 +0900
From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC: <akpm@...ux-foundation.org>, <mgorman@...e.de>,
<hannes@...xchg.org>, <tony.luck@...el.com>,
<matthew.garrett@...ula.com>, <dave@...1.net>, <riel@...hat.com>,
<arjan@...ux.intel.com>, <srinivas.pandruvada@...ux.intel.com>,
<willy@...ux.intel.com>, <kamezawa.hiroyu@...fujitsu.com>,
<lenb@...nel.org>, <rjw@...k.pl>, <gargankita@...il.com>,
<paulmck@...ux.vnet.ibm.com>, <svaidy@...ux.vnet.ibm.com>,
<andi@...stfloor.org>, <santosh.shilimkar@...com>,
<kosaki.motohiro@...il.com>, <linux-pm@...r.kernel.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 06/35] mm: Add helpers to retrieve node region
and zone region for a given page
(2013/08/30 22:15), Srivatsa S. Bhat wrote:
> Given a page, we would like to have an efficient mechanism to find out
> the node memory region and the zone memory region to which it belongs.
>
> Since the node is assumed to be divided into equal-sized node memory
> regions, the node memory region can be obtained by simply right-shifting
> the page's pfn by 'MEM_REGION_SHIFT'.
>
> But finding the corresponding zone memory region's index in the zone is
> not that straight-forward. To have a O(1) algorithm to find it out, define a
> zone_region_idx[] array to store the zone memory region indices for every
> node memory region.
>
> To illustrate, consider the following example:
>
> |<----------------------Node---------------------->|
> __________________________________________________
> | Node mem reg 0 | Node mem reg 1 | (Absolute region
> |________________________|_________________________| boundaries)
>
> __________________________________________________
> | ZONE_DMA | ZONE_NORMAL |
> | | |
> |<--- ZMR 0 --->|<-ZMR0->|<-------- ZMR 1 -------->|
> |_______________|________|_________________________|
>
>
> In the above figure,
>
> Node mem region 0:
> ------------------
> This region corresponds to the first zone mem region in ZONE_DMA and also
> the first zone mem region in ZONE_NORMAL. Hence its index array would look
> like this:
> node_regions[0].zone_region_idx[ZONE_DMA] == 0
> node_regions[0].zone_region_idx[ZONE_NORMAL] == 0
>
>
> Node mem region 1:
> ------------------
> This region corresponds to the second zone mem region in ZONE_NORMAL. Hence
> its index array would look like this:
> node_regions[1].zone_region_idx[ZONE_NORMAL] == 1
>
>
> Using this index array, we can quickly obtain the zone memory region to
> which a given page belongs.
>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> ---
>
> include/linux/mm.h | 24 ++++++++++++++++++++++++
> include/linux/mmzone.h | 7 +++++++
> mm/page_alloc.c | 1 +
> 3 files changed, 32 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 18fdec4..52329d1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -723,6 +723,30 @@ static inline struct zone *page_zone(const struct page *page)
> return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
> }
>
> +static inline int page_node_region_id(const struct page *page,
> + const pg_data_t *pgdat)
> +{
> + return (page_to_pfn(page) - pgdat->node_start_pfn) >> MEM_REGION_SHIFT;
> +}
> +
> +/**
> + * Return the index of the zone memory region to which the page belongs.
> + *
> + * Given a page, find the absolute (node) memory region as well as the zone to
> + * which it belongs. Then find the region within the zone that corresponds to
> + * that node memory region, and return its index.
> + */
> +static inline int page_zone_region_id(const struct page *page)
> +{
> + pg_data_t *pgdat = NODE_DATA(page_to_nid(page));
> + enum zone_type z_num = page_zonenum(page);
> + unsigned long node_region_idx;
> +
> + node_region_idx = page_node_region_id(page, pgdat);
> +
> + return pgdat->node_regions[node_region_idx].zone_region_idx[z_num];
> +}
> +
> #ifdef SECTION_IN_PAGE_FLAGS
> static inline void set_page_section(struct page *page, unsigned long section)
> {
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 010ab5b..76d9ed2 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -726,6 +726,13 @@ struct node_mem_region {
> unsigned long end_pfn;
> unsigned long present_pages;
> unsigned long spanned_pages;
> +
> + /*
> + * A physical (node) region could be split across multiple zones.
> + * Store the indices of the corresponding regions of each such
> + * zone for this physical (node) region.
> + */
> + int zone_region_idx[MAX_NR_ZONES];
You should initialize the zone_region_id[] as negative value.
If the zone_region_id is initialized as 0, region 0 belongs to all zones.
Thanks,
Yasuaki Ishimatsu
> struct pglist_data *pgdat;
> };
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 05cedbb..8ffd47b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4877,6 +4877,7 @@ static void __meminit init_zone_memory_regions(struct pglist_data *pgdat)
> zone_region->present_pages =
> zone_region->spanned_pages - absent;
>
> + node_region->zone_region_idx[zone_idx(z)] = idx;
> idx++;
> }
>
>
--
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