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Message-ID: <AANLkTikCZBLufoL7pH8LKSRZRzOeH0z508PwJ5KwyE-5@mail.gmail.com>
Date: Sun, 17 Oct 2010 12:18:48 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/3] find a contiguous range.
Hi Kame,
Sorry for the late review.
On Wed, Oct 13, 2010 at 12:17 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Unlike memory hotplug, at an allocation of contigous memory range, address
> may not be a problem. IOW, if a requester of memory wants to allocate 100M of
> of contigous memory, placement of allocated memory may not be a problem.
> So, "finding a range of memory which seems to be MOVABLE" is required.
>
> This patch adds a functon to isolate a length of memory within [start, end).
Typo
function
> This function returns a pfn which is 1st page of isolated contigous chunk
Typo
contiguous
> of given length within [start, end).
>
> If no_search=true is passed as argument, start address is always same to
I don't like no_search argument name. It would be better to show not
the implement but context.
How about "bool strict" or "ALLOC_FIXED"?
> the specified "base" addresss.
Typo
address,
Let's add following description.
"Some devices want to bind memory to some memory bank. In this case,
no_search and base address fix
can be helpful."
>
> After isolation, free memory within this area will never be allocated.
> But some pages will remain as "Used/LRU" pages. They should be dropped by
> page reclaim or migration.
At first I saw the above description, I got confused. How about this?
After it isolates some pages in the range, the part of some pages are
freed but others could be used processes now.
Next patch[3/3] try to move or reclaim used pages by page
migration/reclaim for obtaining big contiguous page.
>
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/page_isolation.c | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 130 insertions(+)
>
> Index: mmotm-1008/mm/page_isolation.c
> ===================================================================
> --- mmotm-1008.orig/mm/page_isolation.c
> +++ mmotm-1008/mm/page_isolation.c
> @@ -9,6 +9,7 @@
> #include <linux/pageblock-flags.h>
> #include <linux/memcontrol.h>
> #include <linux/migrate.h>
> +#include <linux/memory_hotplug.h>
> #include <linux/mm_inline.h>
> #include "internal.h"
>
> @@ -254,3 +255,132 @@ out:
> return ret;
> }
>
> +/*
> + * Functions for getting contiguous MOVABLE pages in a zone.
> + */
> +struct page_range {
> + unsigned long base; /* Base address of searching contigouous block */
Typo contiguous.
Please, specify that it's a pfn number.
> + unsigned long end;
> + unsigned long pages;/* Length of contiguous block */
> +};
> +
> +static inline unsigned long MAX_ORDER_ALIGN(unsigned long x)
> +{
> + return ALIGN(x, MAX_ORDER_NR_PAGES);
> +}
> +
> +static inline unsigned long MAX_ORDER_BASE(unsigned long x)
> +{
> + return x & ~(MAX_ORDER_NR_PAGES - 1);
> +}
> +
> +int __get_contig_block(unsigned long pfn, unsigned long nr_pages, void *arg)
> +{
> + struct page_range *blockinfo = arg;
> + unsigned long end;
> +
> + end = pfn + nr_pages;
> + pfn = MAX_ORDER_ALIGN(pfn);
> + end = MAX_ORDER_BASE(end);
> +
> + if (end < pfn)
> + return 0;
> + if (end - pfn >= blockinfo->pages) {
> + blockinfo->base = pfn;
> + blockinfo->end = end;
> + return 1;
> + }
> + return 0;
> +}
> +
> +static void __trim_zone(struct page_range *range)
Hmm..
I think this function name can't present enough meaning.
Let's move description in body of function to the head.
/*
* In most case, each zone's [start_pfn, end_pfn) has no
* overlap between each other. But some arch allows it and
* we need to check it here. If it happens, range end is changed
* to only include pfns in a zone.
*/
> +{
> + struct zone *zone;
> + unsigned long pfn;
> + /*
> + * In most case, each zone's [start_pfn, end_pfn) has no
> + * overlap between each other. But some arch allows it and
> + * we need to check it here.
> + */
> + for (pfn = range->base, zone = page_zone(pfn_to_page(pfn));
> + pfn < range->end;
> + pfn += MAX_ORDER_NR_PAGES) {
> +
> + if (zone != page_zone(pfn_to_page(pfn)))
> + break;
> + }
> + range->end = min(pfn, range->end);
> + return;
Unnecessary return.
> +}
> +
> +/*
> + * This function is for finding a contiguous memory block which has length
> + * of pages and MOVABLE. If it finds, make the range of pages as ISOLATED
> + * and return the first page's pfn.
> + * If no_search==true, this function doesn't scan the range but tries to
> + * isolate the range of memory.
> + */
> +
> +static unsigned long find_contig_block(unsigned long base,
> + unsigned long end, unsigned long pages, bool no_search)
> +{
> + unsigned long pfn, pos;
> + struct page_range blockinfo;
> + int ret;
> +
> + pages = MAX_ORDER_ALIGN(pages);
> +retry:
> + blockinfo.base = base;
> + blockinfo.end = end;
> + blockinfo.pages = pages;
> + /*
> + * At first, check physical page layout and skip memory holes.
> + */
> + ret = walk_system_ram_range(base, end - base, &blockinfo,
> + __get_contig_block);
> + if (!ret)
> + return 0;
> + /* check contiguous pages in a zone */
> + __trim_zone(&blockinfo);
> +
> +
> + /* Ok, we found contiguous memory chunk of size. Isolate it.*/
> + for (pfn = blockinfo.base; pfn + pages < blockinfo.end;
> + pfn += MAX_ORDER_NR_PAGES) {
> + /* If no_search==true, base addess should be same to 'base' */
> + if (no_search && pfn != base)
> + break;
> + /* Better code is necessary here.. */
> + for (pos = pfn; pos < pfn + pages; pos++) {
> + struct page *p;
> +
> + if (!pfn_valid_within(pos))
> + break;
> + p = pfn_to_page(pos);
> + if (PageReserved(p))
> + break;
> + /* This may hit a page on per-cpu queue. */
Couldn't we drain per-cpu queue before this function?
> + if (page_count(p) && !PageLRU(p))
> + break;
> + /* Need to skip order of pages */
> + }
> + if (pos != pfn + pages) {
> + pfn = MAX_ORDER_BASE(pos);
> + continue;
> + }
> + /*
> + * Now, we know [base,end) of a contiguous chunk.
> + * Don't need to take care of memory holes.
> + */
> + if (!start_isolate_page_range(pfn, pfn + pages))
> + return pfn;
> + }
> +
> + /* failed */
> + if (!no_search && blockinfo.end + pages < end) {
> + /* Move base address and find the next block of RAM. */
> + base = blockinfo.end;
> + goto retry;
> + }
> + return 0;
> +}
>
>
--
Kind regards,
Minchan Kim
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