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Subject: Re: [PATCH v2 2/4] mm: remove zone_lru_lock() function access
 ->lru_lock directly
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>
CC:     Johannes Weiner <hannes@cmpxchg.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Rik van Riel <riel@surriel.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>
References: <20190228083329.31892-1-aryabinin@virtuozzo.com>
 <20190228083329.31892-2-aryabinin@virtuozzo.com>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <44ffadb4-4235-76c9-332f-680dda5da521@nvidia.com>
Date:   Thu, 28 Feb 2019 13:44:40 -0800
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On 2/28/19 12:33 AM, Andrey Ryabinin wrote:
> We have common pattern to access lru_lock from a page pointer:
> 	zone_lru_lock(page_zone(page))
> 
> Which is silly, because it unfolds to this:
> 	&NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)]->zone_pgdat->lru_lock
> while we can simply do
> 	&NODE_DATA(page_to_nid(page))->lru_lock
> 

Hi Andrey,

Nice. I like it so much that I immediately want to tweak it. :)


> Remove zone_lru_lock() function, since it's only complicate things.
> Use 'page_pgdat(page)->lru_lock' pattern instead.

Here, I think the zone_lru_lock() is actually a nice way to add
a touch of clarity at the call sites. How about, see below:

[snip]

> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2fd4247262e9..22423763c0bd 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -788,10 +788,6 @@ typedef struct pglist_data {
>  
>  #define node_start_pfn(nid)	(NODE_DATA(nid)->node_start_pfn)
>  #define node_end_pfn(nid) pgdat_end_pfn(NODE_DATA(nid))
> -static inline spinlock_t *zone_lru_lock(struct zone *zone)
> -{
> -	return &zone->zone_pgdat->lru_lock;
> -}
>  

Instead of removing that function, let's change it, and add another
(since you have two cases: either a page* or a pgdat* is available),
and move it to where it can compile, like this:


diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80bb6408fe73..cea3437f5d68 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1167,6 +1167,16 @@ static inline pg_data_t *page_pgdat(const struct page *page)
        return NODE_DATA(page_to_nid(page));
 }
 
+static inline spinlock_t *zone_lru_lock(pg_data_t *pgdat)
+{
+       return &pgdat->lru_lock;
+}
+
+static inline spinlock_t *zone_lru_lock_from_page(struct page *page)
+{
+       return zone_lru_lock(page_pgdat(page));
+}
+
 #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 842f9189537b..e03042fe1d88 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -728,11 +728,6 @@ typedef struct pglist_data {
 
 #define node_start_pfn(nid)    (NODE_DATA(nid)->node_start_pfn)
 #define node_end_pfn(nid) pgdat_end_pfn(NODE_DATA(nid))
-static inline spinlock_t *zone_lru_lock(struct zone *zone)
-{
-       return &zone->zone_pgdat->lru_lock;
-}
-
 static inline struct lruvec *node_lruvec(struct pglist_data *pgdat)
 {
        return &pgdat->lruvec;


Like it?

thanks,
-- 
John Hubbard
NVIDIA