Re: [RFC 4/4] Sparse initialization of struct page array.

[Robin Holt <holt@sgi.com>]

On Thu, Jul 25, 2013 at 05:50:57AM -0700, Yinghai Lu wrote:
> On Wed, Jul 24, 2013 at 7:25 PM, Robin Holt <holt@sgi.com> wrote:
> >>
> >> How about holes that is not in memblock.reserved?
> >>
> >> before this patch:
> >> free_area_init_node/free_area_init_core/memmap_init_zone
> >> will mark all page in node range to Reserved in struct page, at first.
> >>
> >> but those holes is not mapped via kernel low mapping.
> >> so it should be ok not touch "struct page" for them.
> >>
> >> Now you only mark reserved for memblock.reserved at first, and later
> >> mark {memblock.memory} - { memblock.reserved} to be available.
> >> And that is ok.
> >>
> >> but should split that change to another patch and add some comment
> >> and change log for the change.
> >> in case there is some user like UEFI etc do weird thing.
> >
> > Nate and I talked this over today.  Sorry for the delay, but it was the
> > first time we were both free.  Neither of us quite understands what you
> > are asking for here.  My interpretation is that you would like us to
> > change the use of the PageReserved flag such that during boot, we do not
> > set the flag at all from memmap_init_zone, and then only set it on pages
> > which, at the time of free_all_bootmem, have been allocated/reserved in
> > the memblock allocator.  Is that correct?  I will start to work that up
> > on the assumption that is what you are asking for.
> 
> Not exactly.
> 
> your change should be right, but there is some subtle change about
> holes handling.
> 
> before mem holes between memory ranges in memblock.memory, get struct page,
> and initialized with to Reserved in memmap_init_zone.
> Those holes is not in memory.reserved, with your patches, those hole's
> struct page
> will still have all 0.
> 
> Please separate change about set page to reserved according to memory.reserved
> to another patch.


Just want to make sure this is where you want me to go.  Here is my
currently untested patch.  Is that what you were expecting to have done?
One thing I don't like about this patch is it seems to slow down boot in
my simulator environment.  I think I am going to look at restructuring
things a bit to see if I can eliminate that performance penalty.
Otherwise, I think I am following your directions.

Thanks,
Robin Holt

>From bdd2fefa59af18f283af6f066bc644ddfa5c7da8 Mon Sep 17 00:00:00 2001
From: Robin Holt <holt@sgi.com>
Date: Thu, 25 Jul 2013 04:25:15 -0500
Subject: [RFC -v2-pre2 4/5] ZZZ Only SegPageReserved() on memblock reserved
 pages.

---
 include/linux/mm.h |  2 ++
 mm/nobootmem.c     |  3 +++
 mm/page_alloc.c    | 18 +++++++++++-------
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e0c8528..b264a26 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1322,6 +1322,8 @@ static inline void adjust_managed_page_count(struct page *page, long count)
 	totalram_pages += count;
 }
 
+extern void reserve_bootmem_region(unsigned long start, unsigned long end);
+
 /* Free the reserved page into the buddy system, so it gets managed. */
 static inline void __free_reserved_page(struct page *page)
 {
diff --git a/mm/nobootmem.c b/mm/nobootmem.c
index 2159e68..0840af2 100644
--- a/mm/nobootmem.c
+++ b/mm/nobootmem.c
@@ -117,6 +117,9 @@ static unsigned long __init free_low_memory_core_early(void)
 	phys_addr_t start, end, size;
 	u64 i;
 
+	for_each_reserved_mem_region(i, &start, &end)
+		reserve_bootmem_region(start, end);
+
 	for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL)
 		count += __free_memory_core(start, end);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 048e166..3aa30b7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -698,7 +698,7 @@ static void free_one_page(struct zone *zone, struct page *page, int order,
 }
 
 static void __init_single_page(unsigned long pfn, unsigned long zone,
-			       int nid, int reserved)
+			       int nid, int page_count)
 {
 	struct page *page = pfn_to_page(pfn);
 	struct zone *z = &NODE_DATA(nid)->node_zones[zone];
@@ -708,12 +708,9 @@ static void __init_single_page(unsigned long pfn, unsigned long zone,
 	init_page_count(page);
 	page_mapcount_reset(page);
 	page_nid_reset_last(page);
-	if (reserved) {
-		SetPageReserved(page);
-	} else {
-		ClearPageReserved(page);
-		set_page_count(page, 0);
-	}
+	ClearPageReserved(page);
+	set_page_count(page, page_count);
+
 	/*
 	 * Mark the block movable so that blocks are reserved for
 	 * movable at startup. This will force kernel allocations
@@ -741,6 +738,13 @@ static void __init_single_page(unsigned long pfn, unsigned long zone,
 #endif
 }
 
+void reserve_bootmem_region(unsigned long start, unsigned long end)
+{
+	for (; start < end; start++)
+		if (pfn_valid(start))
+			SetPageReserved(pfn_to_page(start));
+}
+
 static bool free_pages_prepare(struct page *page, unsigned int order)
 {
 	int i;
-- 
1.8.2.1