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Message-Id: <20130204160624.5c20a8a0.akpm@linux-foundation.org>
Date: Mon, 4 Feb 2013 16:06:24 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lin Feng <linfeng@...fujitsu.com>
Cc: mgorman@...e.de, bcrl@...ck.org, viro@...iv.linux.org.uk,
khlebnikov@...nvz.org, walken@...gle.com,
kamezawa.hiroyu@...fujitsu.com, minchan@...nel.org,
riel@...hat.com, rientjes@...gle.com,
isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
laijs@...fujitsu.com, jiang.liu@...wei.com, linux-mm@...ck.org,
linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: hotplug: implement non-movable version of
get_user_pages() called get_user_pages_non_movable()
melreadthis
On Mon, 4 Feb 2013 18:04:07 +0800
Lin Feng <linfeng@...fujitsu.com> wrote:
> get_user_pages() always tries to allocate pages from movable zone, which is not
> reliable to memory hotremove framework in some case.
>
> This patch introduces a new library function called get_user_pages_non_movable()
> to pin pages only from zone non-movable in memory.
> It's a wrapper of get_user_pages() but it makes sure that all pages come from
> non-movable zone via additional page migration.
>
> ...
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1049,6 +1049,11 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> struct page **pages, struct vm_area_struct **vmas);
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> struct page **pages);
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +int get_user_pages_non_movable(struct task_struct *tsk, struct mm_struct *mm,
> + unsigned long start, int nr_pages, int write, int force,
> + struct page **pages, struct vm_area_struct **vmas);
> +#endif
The ifdefs aren't really needed here and I encourage people to omit
them. This keeps the header files looking neater and reduces the
chances of things later breaking because we forgot to update some
CONFIG_foo logic in a header file. The downside is that errors will be
revealed at link time rather than at compile time, but that's a pretty
small cost.
> struct kvec;
> int get_kernel_pages(const struct kvec *iov, int nr_pages, int write,
> struct page **pages);
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 73b64a3..5db811e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -838,6 +838,10 @@ static inline int is_normal_idx(enum zone_type idx)
> return (idx == ZONE_NORMAL);
> }
>
> +static inline int is_movable(struct zone *zone)
> +{
> + return zone == zone->zone_pgdat->node_zones + ZONE_MOVABLE;
> +}
A better name would be zone_is_movable(). We haven't been very
consistent about this in mmzone.h, but zone_is_foo() is pretty common.
And a neater implementation would be
return zone_idx(zone) == ZONE_MOVABLE;
All of which made me look at mmzone.h, and what I saw wasn't very nice :(
Please review...
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: include/linux/mmzone.h: cleanups
- implement zone_idx() in C to fix its references-args-twice macro bug
- use zone_idx() in is_highmem() to remove large amounts of silly fluff.
Cc: Lin Feng <linfeng@...fujitsu.com>
Cc: Mel Gorman <mel@....ul.ie>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
include/linux/mmzone.h | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff -puN include/linux/mmzone.h~include-linux-mmzoneh-cleanups include/linux/mmzone.h
--- a/include/linux/mmzone.h~include-linux-mmzoneh-cleanups
+++ a/include/linux/mmzone.h
@@ -815,7 +815,10 @@ unsigned long __init node_memmap_size_by
/*
* zone_idx() returns 0 for the ZONE_DMA zone, 1 for the ZONE_NORMAL zone, etc.
*/
-#define zone_idx(zone) ((zone) - (zone)->zone_pgdat->node_zones)
+static inline enum zone_type zone_idx(struct zone *zone)
+{
+ return zone - zone->zone_pgdat->node_zones;
+}
static inline int populated_zone(struct zone *zone)
{
@@ -857,10 +860,10 @@ static inline int is_normal_idx(enum zon
static inline int is_highmem(struct zone *zone)
{
#ifdef CONFIG_HIGHMEM
- int zone_off = (char *)zone - (char *)zone->zone_pgdat->node_zones;
- return zone_off == ZONE_HIGHMEM * sizeof(*zone) ||
- (zone_off == ZONE_MOVABLE * sizeof(*zone) &&
- zone_movable_is_highmem());
+ enum zone_type idx = zone_idx(zone);
+
+ return idx == ZONE_HIGHMEM ||
+ (idx == ZONE_MOVABLE && zone_movable_is_highmem());
#else
return 0;
#endif
_
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -58,6 +58,8 @@
> #include <linux/elf.h>
> #include <linux/gfp.h>
> #include <linux/migrate.h>
> +#include <linux/page-isolation.h>
> +#include <linux/mm_inline.h>
> #include <linux/string.h>
>
> #include <asm/io.h>
> @@ -1995,6 +1997,67 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> }
> EXPORT_SYMBOL(get_user_pages);
>
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +/**
> + * It's a wrapper of get_user_pages() but it makes sure that all pages come from
> + * non-movable zone via additional page migration.
> + */
This needs a description of why the function exists - say something
about the requirements of memory hotplug.
Also a few words describing how the function works would be good.
> +int get_user_pages_non_movable(struct task_struct *tsk, struct mm_struct *mm,
> + unsigned long start, int nr_pages, int write, int force,
> + struct page **pages, struct vm_area_struct **vmas)
> +{
> + int ret, i, isolate_err, migrate_pre_flag;
> + LIST_HEAD(pagelist);
> +
> +retry:
> + ret = get_user_pages(tsk, mm, start, nr_pages, write, force, pages,
> + vmas);
We should handle (ret < 0) here. At present the function will silently
convert an error return into "return 0", which is bad. The function
does appear to otherwise do the right thing if get_user_pages() failed,
but only due to good luck.
> + isolate_err = 0;
> + migrate_pre_flag = 0;
> +
> + for (i = 0; i < ret; i++) {
> + if (is_movable(page_zone(pages[i]))) {
> + if (!migrate_pre_flag) {
> + if (migrate_prep())
> + goto put_page;
> + migrate_pre_flag = 1;
> + }
> +
> + if (!isolate_lru_page(pages[i])) {
> + inc_zone_page_state(pages[i], NR_ISOLATED_ANON +
> + page_is_file_cache(pages[i]));
> + list_add_tail(&pages[i]->lru, &pagelist);
> + } else {
> + isolate_err = 1;
> + goto put_page;
> + }
> + }
> + }
> +
> + /* All pages are non movable, we are done :) */
> + if (i == ret && list_empty(&pagelist))
> + return ret;
> +
> +put_page:
> + /* Undo the effects of former get_user_pages(), we won't pin anything */
> + for (i = 0; i < ret; i++)
> + put_page(pages[i]);
> +
> + if (migrate_pre_flag && !isolate_err) {
> + ret = migrate_pages(&pagelist, alloc_migrate_target, 1,
> + false, MIGRATE_SYNC, MR_SYSCALL);
> + /* Steal pages from non-movable zone successfully? */
> + if (!ret)
> + goto retry;
This is buggy. migrate_pages() doesn't empty its `from' argument, so
page_list must be reinitialised here (or, better, at the start of the loop).
Mel, what's up with migrate_pages()? Shouldn't it be removing the
pages from the list when MIGRATEPAGE_SUCCESS? The use of
list_for_each_entry_safe() suggests we used to do that...
> + }
> +
> + putback_lru_pages(&pagelist);
> + return 0;
> +}
> +EXPORT_SYMBOL(get_user_pages_non_movable);
> +#endif
> +
Generally, I'd like Mel to go through (the next version of) this patch
carefully, please.
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