Re: [PATCH] mm, page_alloc: calculate first_deferred_pfn directly

Andrew Morton
2018-12-20T23:04:56Z

Does anyone care to review this one?

Thanks.

From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/page_alloc.c: calculate first_deferred_pfn directly

After c9e97a1997fb ("mm: initialize pages on demand during boot"), the
behavior of DEFERRED_STRUCT_PAGE_INIT is changed to initialize the first
section for the highest zone on each node.

Instead of testing each pfn during the iteration, we can calculate the
first_deferred_pfn directly with necessary information.

By doing so, we also get some performance benefit during bootup:

+----------+-----------+-----------+--------+
| |Base |Patched |Gain |
+----------+-----------+-----------+--------+
| 1 Node |0.011993 |0.011459 |-4.45% |
+----------+-----------+-----------+--------+
| 4 Nodes |0.006466 |0.006255 |-3.26% |
+----------+-----------+-----------+--------+

Test result is retrieved from dmesg time stamp by add printk around
free_area_init_nodes().

Link: http://lkml.kernel.org/r/20181207100859.8999-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Pasha Tatashin <Pavel.Tatashin@microsoft.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <OSalvador@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/page_alloc.c | 57 +++++++++++++++++++++-------------------------
1 file changed, 27 insertions(+), 30 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-calculate-first_deferred_pfn-directly
+++ a/mm/page_alloc.c
@@ -306,38 +306,33 @@ static inline bool __meminit early_page_
}

/*
- * Returns true when the remaining initialisation should be deferred until
- * later in the boot cycle when it can be parallelised.
+ * Calculate first_deferred_pfn in case:
+ * - in MEMMAP_EARLY context
+ * - this is the last zone
+ *
+ * If the first aligned section doesn't exceed the end_pfn, set it to
+ * first_deferred_pfn and return it.
*/
-static bool __meminit
-defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
+unsigned long __meminit
+defer_pfn(int nid, unsigned long start_pfn, unsigned long end_pfn,
+ enum memmap_context context)
{
- static unsigned long prev_end_pfn, nr_initialised;
+ struct pglist_data *pgdat = NODE_DATA(nid);
+ unsigned long pfn;

- /*
- * prev_end_pfn static that contains the end of previous zone
- * No need to protect because called very early in boot before smp_init.
- */
- if (prev_end_pfn != end_pfn) {
- prev_end_pfn = end_pfn;
- nr_initialised = 0;
- }
+ if (context != MEMMAP_EARLY)
+ return end_pfn;

- /* Always populate low zones for address-constrained allocations */
- if (end_pfn < pgdat_end_pfn(NODE_DATA(nid)))
- return false;
+ /* Always populate low zones */
+ if (end_pfn < pgdat_end_pfn(pgdat))
+ return end_pfn;

- /*
- * We start only with one section of pages, more pages are added as
- * needed until the rest of deferred pages are initialized.
- */
- nr_initialised++;
- if ((nr_initialised > PAGES_PER_SECTION) &&
- (pfn & (PAGES_PER_SECTION - 1)) == 0) {
- NODE_DATA(nid)->first_deferred_pfn = pfn;
- return true;
+ pfn = roundup(start_pfn + PAGES_PER_SECTION - 1, PAGES_PER_SECTION);
+ if (end_pfn > pfn) {
+ pgdat->first_deferred_pfn = pfn;
+ end_pfn = pfn;
}
- return false;
+ return end_pfn;
}
#else
static inline bool early_page_uninitialised(unsigned long pfn)
@@ -345,9 +340,11 @@ static inline bool early_page_uninitiali
return false;
}

-static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
+unsigned long __meminit
+defer_pfn(int nid, unsigned long start_pfn, unsigned long end_pfn,
+ enum memmap_context context)
{
- return false;
+ return end_pfn;
}
#endif

@@ -5785,6 +5782,8 @@ void __meminit memmap_init_zone(unsigned
return;
}

+ end_pfn = defer_pfn(nid, start_pfn, end_pfn, context);
+
for (pfn = start_pfn; pfn < end_pfn; pfn++) {
struct page *page;

@@ -5798,8 +5797,6 @@ void __meminit memmap_init_zone(unsigned
continue;
if (overlap_memmap_init(zone, &pfn))
continue;
- if (defer_init(nid, pfn, end_pfn))
- break;

page = pfn_to_page(pfn);
__init_single_page(page, pfn, zone, nid);
_