On Wed, 9 May 2007, Yasunori Goto wrote:
This patch is for supporting making page unused.
Without reading the patch, this could also be interesting when trying to
free a block of pages for a contiguous allocation without racing against
other allocators.
Isolate pages by capturing freed pages before inserting free_area[],
buddy allocator.
If you have an idea for avoiding spin_lock(), please advise me.
Again, commenting on this before I read the patch. Grouping pages by
mobility uses a bitmap to track flags affecting a block of pages. If you
used a bit there and added a MIGRATE_ISOLATING type, the pages on free
would get placed in those freelists. As long as MIGRATE_ISOLATING is not
in fallbacks[] in page_alloc.c, the pages would not get allocated. This
should avoid the need for a separate spinlock.
That said, it increases the size of struct zone more than yours do and
ties these patches to a part of grouping pages by mobility which you don't
do currently.
Isolating pages in free_area[] is implemented in other patch.
I haven't seen that part yet but it sounds like it does something similar
to move_freepages() so there may be code to be shared there.
Signed-Off-By: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Yasunori Goto <[email protected]>
include/linux/mmzone.h | 8 +
include/linux/page_isolation.h | 52 +++++++++++
mm/Kconfig | 7 +
mm/page_alloc.c | 187 +++++++++++++++++++++++++++++++++++++++++
4 files changed, 254 insertions(+)
Index: current_test/include/linux/mmzone.h
===================================================================
--- current_test.orig/include/linux/mmzone.h 2007-05-08 15:06:49.000000000 +0900
+++ current_test/include/linux/mmzone.h 2007-05-08 15:08:03.000000000 +0900
@@ -314,6 +314,14 @@ struct zone {
/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
unsigned long zone_start_pfn;
+#ifdef CONFIG_PAGE_ISOLATION
+ /*
+ * For pages which are not used but not free.
+ * See include/linux/page_isolation.h
+ */
+ spinlock_t isolation_lock;
+ struct list_head isolation_list;
+#endif
Using MIGRATE_ISOLATING instead of this approach does mean that there will
be MAX_ORDER additional struct free_area added to the zone. That is more
lists than this approach.
I am somewhat suprised that CONFIG_PAGE_ISOLATION exists as a separate
option. If it was a compile-time option at all, I would expect it to
depend on memory hot-remove being selected.
/*
* zone_start_pfn, spanned_pages and present_pages are all
* protected by span_seqlock. It is a seqlock because it has
Index: current_test/mm/page_alloc.c
===================================================================
--- current_test.orig/mm/page_alloc.c 2007-05-08 15:07:20.000000000 +0900
+++ current_test/mm/page_alloc.c 2007-05-08 15:08:34.000000000 +0900
@@ -41,6 +41,7 @@
#include <linux/pfn.h>
#include <linux/backing-dev.h>
#include <linux/fault-inject.h>
+#include <linux/page_isolation.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
@@ -448,6 +449,9 @@ static inline void __free_one_page(struc
if (unlikely(PageCompound(page)))
destroy_compound_page(page, order);
+ if (page_under_isolation(zone, page, order))
+ return;
+
Using MIGRATE_ISOLATING would avoid a potential list search here.
page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
VM_BUG_ON(page_idx & (order_size - 1));
@@ -3259,6 +3263,10 @@ static void __meminit free_area_init_cor
zone->nr_scan_inactive = 0;
zap_zone_vm_stats(zone);
atomic_set(&zone->reclaim_in_progress, 0);
+#ifdef CONFIG_PAGE_ISOLATION
+ spin_lock_init(&zone->isolation_lock);
+ INIT_LIST_HEAD(&zone->isolation_list);
i> +#endif
if (!size)
continue;
@@ -4214,3 +4222,182 @@ void set_pageblock_flags_group(struct pa
else
__clear_bit(bitidx + start_bitidx, bitmap);
}
+
+#ifdef CONFIG_PAGE_ISOLATION
+/*
+ * Page Isolation.
+ *
+ * If a page is removed from usual free_list and will never be used,
+ * It is linked to "struct isolation_info" and set Reserved, Private
+ * bit. page->mapping points to isolation_info in it.
+ * and page_count(page) is 0.
+ *
+ * This can be used for creating a chunk of contiguous *unused* memory.
+ *
+ * current user is Memory-Hot-Remove.
+ * maybe move to some other file is better.
page_isolation.c to match the header filename seems reasonable.
page_alloc.c has a lot of multi-function stuff like memory initialisation
in it.
+ */
+static void
+isolate_page_nolock(struct isolation_info *info, struct page *page, int order)
+{
+ int pagenum;
+ pagenum = 1 << order;
+ while (pagenum > 0) {
+ SetPageReserved(page);
+ SetPagePrivate(page);
+ page->private = (unsigned long)info;
+ list_add(&page->lru, &info->pages);
+ page++;
+ pagenum--;
+ }
+}
It's worth commenting somewhere that pages on the list in isolation_info
are always order-0.
+
+/*
+ * This function is called from page_under_isolation()
+ */
+
+int __page_under_isolation(struct zone *zone, struct page *page, int order)
+{
+ struct isolation_info *info;
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long flags;
+ int found = 0;
+
+ spin_lock_irqsave(&zone->isolation_lock,flags);
An unwritten convention seems to be that __ versions of same-named
functions are the nolock version. i.e. I would expect
page_under_isolation() to acquire and release the spinlock and
__page_under_isolation() to do no additional locking.
Locking outside of here might make the flow a little clearer as well if
you had two returns and avoided the use of "found".
+ list_for_each_entry(info, &zone->isolation_list, list) {
+ if (info->start_pfn <= pfn && pfn < info->end_pfn) {
+ found = 1;
+ break;
+ }
+ }
+ if (found) {
+ isolate_page_nolock(info, page, order);
+ }
+ spin_unlock_irqrestore(&zone->isolation_lock, flags);
+ return found;
+}
+
+/*
+ * start and end must be in the same zone.
+ *
+ */
+struct isolation_info *
+register_isolation(unsigned long start, unsigned long end)
+{
+ struct zone *zone;
+ struct isolation_info *info = NULL, *tmp;
+ unsigned long flags;
+ unsigned long last_pfn = end - 1;
+
+ if (!pfn_valid(start) || !pfn_valid(last_pfn) || (start >= end))
+ return ERR_PTR(-EINVAL);
+ /* check start and end is in the same zone */
+ zone = page_zone(pfn_to_page(start));
+
+ if (zone != page_zone(pfn_to_page(last_pfn)))
+ return ERR_PTR(-EINVAL);
+ /* target range has to match MAX_ORDER alignmet */
+ if ((start & (MAX_ORDER_NR_PAGES - 1)) ||
+ (end & (MAX_ORDER_NR_PAGES - 1)))
+ return ERR_PTR(-EINVAL);
Why does the range have to be MAX_ORDER alighned?
+ info = kmalloc(sizeof(*info), GFP_KERNEL);
+ if (!info)
+ return ERR_PTR(-ENOMEM);
+ spin_lock_irqsave(&zone->isolation_lock, flags);
+ /* we don't allow overlap among isolation areas */
+ if (!list_empty(&zone->isolation_list)) {
+ list_for_each_entry(tmp, &zone->isolation_list, list) {
+ if (start < tmp->end_pfn && end > tmp->start_pfn) {
+ goto out_free;
+ }
+ }
+ }
Why not merge requests for overlapping isolations?
+ info->start_pfn = start;
+ info->end_pfn = end;
+ info->zone = zone;
+ INIT_LIST_HEAD(&info->list);
+ INIT_LIST_HEAD(&info->pages);
+ list_add(&info->list, &zone->isolation_list);
+out_unlock:
+ spin_unlock_irqrestore(&zone->isolation_lock, flags);
+ return info;
+out_free:
+ kfree(info);
+ info = ERR_PTR(-EBUSY);
+ goto out_unlock;
+}
+/*
+ * Remove IsolationInfo from zone.
+ * After this, we can unuse memory in info or
+ * free back to freelist.
+ */
+
+void
+detach_isolation_info_zone(struct isolation_info *info)
+{
+ unsigned long flags;
+ struct zone *zone = info->zone;
+ spin_lock_irqsave(&zone->isolation_lock,flags);
+ list_del(&info->list);
+ info->zone = NULL;
+ spin_unlock_irqrestore(&zone->isolation_lock,flags);
+}
+
+/*
+ * All pages in info->pages should be remvoed before calling this.
+ * And info should be detached from zone.
+ */
+void
+free_isolation_info(struct isolation_info *info)
+{
+ BUG_ON(!list_empty(&info->pages));
+ BUG_ON(info->zone);
+ kfree(info);
+ return;
+}
+
+/*
+ * Mark All pages in the isolation_info to be Reserved.
+ * When onlining these pages again, a user must check
+ * which page is usable by IORESOURCE_RAM
+ * please see memory_hotplug.c/online_pages() if unclear.
+ *
+ * info should be detached from zone before calling this.
+ */
+void
+unuse_all_isolated_pages(struct isolation_info *info)
+{
+ struct page *page, *n;
+ BUG_ON(info->zone);
+ list_for_each_entry_safe(page, n, &info->pages, lru) {
+ SetPageReserved(page);
+ page->private = 0;
+ ClearPagePrivate(page);
+ list_del(&page->lru);
+ }
+}
+
+/*
+ * Free all pages connected in isolation list.
+ * pages are moved back to free_list.
+ */
+void
+free_all_isolated_pages(struct isolation_info *info)
+{
+ struct page *page, *n;
+ BUG_ON(info->zone);
+ list_for_each_entry_safe(page, n ,&info->pages, lru) {
+ ClearPagePrivate(page);
+ ClearPageReserved(page);
+ page->private = 0;
+ list_del(&page->lru);
+ set_page_count(page, 0);
+ set_page_refcounted(page);
+ /* This is sage because info is detached from zone */
s/sage/safe/
+ __free_page(page);
+ }
+}
+
+#endif /* CONFIG_PAGE_ISOLATION */
+
+
Index: current_test/mm/Kconfig
===================================================================
--- current_test.orig/mm/Kconfig 2007-05-08 15:06:50.000000000 +0900
+++ current_test/mm/Kconfig 2007-05-08 15:08:31.000000000 +0900
@@ -225,3 +225,10 @@ config DEBUG_READAHEAD
Say N for production servers.
+config PAGE_ISOLATION
+ bool "Page Isolation Framework"
+ help
+ This option adds page isolation framework to mm.
+ This is used for isolate amount of contiguous pages from linux
+ memory management.
+ Say N if unsure.
Index: current_test/include/linux/page_isolation.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ current_test/include/linux/page_isolation.h 2007-05-08 15:08:34.000000000 +0900
@@ -0,0 +1,52 @@
+#ifndef __LINIX_PAGE_ISOLATION_H
+#define __LINUX_PAGE_ISOLATION_H
+
+#ifdef CONFIG_PAGE_ISOLATION
+
+struct isolation_info {
+ struct list_head list;
+ unsigned long start_pfn;
+ unsigned long end_pfn;
+ struct zone *zone;
+ struct list_head pages;
+};
+
+extern int
+__page_under_isolation(struct zone *zone, struct page *page, int order);
+
+static inline int
+page_under_isolation(struct zone *zone, struct page *page, int order)
+{
+ if (likely(list_empty(&zone->isolation_list)))
+ return 0;
+ return __page_under_isolation(zone, page, order);
+}
+
+static inline int
+is_page_isolated(struct isolation_info *info, struct page *page)
+{
+ if (PageReserved(page) && PagePrivate(page) &&
+ page_count(page) == 0 &&
+ page->private == (unsigned long)info)
+ return 1;
+ return 0;
+}
+
+extern struct isolation_info *
+register_isolation(unsigned long start, unsigned long end);
+
+extern void detach_isolation_info_zone(struct isolation_info *info);
+extern void free_isolation_info(struct isolation_info *info);
+extern void unuse_all_isolated_pages(struct isolation_info *info);
+extern void free_all_isolated_pages(struct isolation_info *info);
+
+#else
+
+static inline int
+page_under_isolation(struct zone *zone, struct page *page, int order)
+{
+ return 0;
+}
+
+#endif
+#endif
--
Yasunori Goto
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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