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Message-ID: <AANLkTinvmJNAXAKFbSZvhyPAbZsEW1eBY2YDkqvr5FF5@mail.gmail.com>
Date: Mon, 22 Nov 2010 20:20:14 +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>,
Bob Liu <lliubbo@...il.com>, fujita.tomonori@....ntt.co.jp,
m.nazarewicz@...sung.com, pawel@...iak.com, andi.kleen@...el.com,
felipe.contreras@...il.com,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH 2/4] alloc_contig_pages() find appropriate physical memory range
On Fri, Nov 19, 2010 at 5:14 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).
> This function returns a pfn which is 1st page of isolated contigous chunk
> of given length within [start, end).
>
> If no_search=true is passed as argument, start address is always same to
> the specified "base" addresss.
>
> 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.
>
> Changelog: 2010-11-17
> - fixed some conding style (if-then-else)
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/page_isolation.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 146 insertions(+)
>
> Index: mmotm-1117/mm/page_isolation.c
> ===================================================================
> --- mmotm-1117.orig/mm/page_isolation.c
> +++ mmotm-1117/mm/page_isolation.c
> @@ -7,6 +7,7 @@
> #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"
>
> @@ -250,3 +251,148 @@ int do_migrate_range(unsigned long start
> out:
> return ret;
> }
> +
> +/*
> + * Functions for getting contiguous MOVABLE pages in a zone.
> + */
> +struct page_range {
> + unsigned long base; /* Base address of searching contigouous block */
> + unsigned long end;
> + unsigned long pages;/* Length of contiguous block */
Nitpick.
You used nr_pages in other place.
I hope you use the name consistent.
> + int align_order;
> + unsigned long align_mask;
Does we really need this field 'align_mask'?
We can get always from align_order.
> +};
> +
> +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 = ALIGN(pfn, 1 << blockinfo->align_order);
> + end = end & ~(MAX_ORDER_NR_PAGES - 1);
> +
> + 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 zone *zone, struct page_range *range)
> +{
> + unsigned long pfn;
> + /*
> + * skip pages which dones'nt under the zone.
typo dones'nt -> doesn't :)
> + * There are some archs which zones are not in linear layout.
> + */
> + if (page_zone(pfn_to_page(range->base)) != zone) {
> + for (pfn = range->base;
> + pfn < range->end;
> + pfn += MAX_ORDER_NR_PAGES) {
> + if (page_zone(pfn_to_page(pfn)) == zone)
> + break;
> + }
> + range->base = min(pfn, range->end);
> + }
> + /* Here, range-> base is in the zone if range->base != range->end */
> + for (pfn = range->base;
> + pfn < range->end;
> + pfn += MAX_ORDER_NR_PAGES) {
> + if (zone != page_zone(pfn_to_page(pfn))) {
> + pfn = pfn - MAX_ORDER_NR_PAGES;
> + break;
> + }
> + }
> + range->end = min(pfn, range->end);
> + return;
Remove 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.
> + * This checks all pages in the returned range is free of Pg_LRU. To reduce
> + * the risk of false-positive testing, lru_add_drain_all() should be called
> + * before this function to reduce pages on pagevec for zones.
> + */
> +
> +static unsigned long find_contig_block(unsigned long base,
> + unsigned long end, unsigned long pages,
> + int align_order, struct zone *zone)
> +{
> + unsigned long pfn, pos;
> + struct page_range blockinfo;
> + int ret;
> +
> + VM_BUG_ON(pages & (MAX_ORDER_NR_PAGES - 1));
> + VM_BUG_ON(base & ((1 << align_order) - 1));
> +retry:
> + blockinfo.base = base;
> + blockinfo.end = end;
> + blockinfo.pages = pages;
> + blockinfo.align_order = align_order;
> + blockinfo.align_mask = (1 << align_order) - 1;
We don't need this.
> + /*
> + * 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(zone, &blockinfo);
> +
> + /*
> + * Ok, we found contiguous memory chunk of size. Isolate it.
> + * We just search MAX_ORDER aligned range.
> + */
> + for (pfn = blockinfo.base; pfn + pages <= blockinfo.end;
> + pfn += (1 << align_order)) {
> + struct zone *z = page_zone(pfn_to_page(pfn));
> + if (z != zone)
> + continue;
Could we make sure pass __trim_zone is to satisfy whole pfn in zone
what we want.
Repeated the zone check is rather annoying.
I mean let's __get_contig_block or __trim_zone already does check zone
so that we remove the zone check in here.
> +
> + spin_lock_irq(&z->lock);
> + pos = pfn;
> + /*
> + * Check the range only contains free pages or LRU pages.
> + */
> + while (pos < pfn + pages) {
> + struct page *p;
> +
> + if (!pfn_valid_within(pos))
> + break;
> + p = pfn_to_page(pos);
> + if (PageReserved(p))
> + break;
> + if (!page_count(p)) {
> + if (!PageBuddy(p))
> + pos++;
> + else
> + pos += (1 << page_order(p));
> + } else if (PageLRU(p)) {
Could we check get_pageblock_migratetype(page) == MIGRATE_MOVABLE in
here and early bail out?
> + pos++;
> + } else
> + break;
> + }
> + spin_unlock_irq(&z->lock);
> + if ((pos == pfn + pages)) {
> + if (!start_isolate_page_range(pfn, pfn + pages))
> + return pfn;
> + } else/* the chunk including "pos" should be skipped */
> + pfn = pos & ~((1 << align_order) - 1);
> + cond_resched();
> + }
> +
> + /* failed */
> + if (blockinfo.end + pages <= end) {
> + /* Move base address and find the next block of RAM. */
> + base = blockinfo.end;
> + goto retry;
> + }
> + return 0;
If the base is 0, isn't it impossible return pfn 0?
x86 in FLAT isn't impossible but I think some architecture might be possible.
Just guessing.
How about returning negative value and return first page pfn and last
page pfn as out parameter base, end?
> +}
>
>
--
Kind regards,
Minchan Kim
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