Re: [PATCH] Have __free_pages_memory() free in larger chunks.

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Tue, Sep 10, 2013 at 01:57:24PM -0500, Nathan Zimmer wrote:
>From: Robin Holt <robin.m.holt@gmail.com>
>
>On large memory machines it can take a few minutes to get through
>free_all_bootmem().
>
>Currently, when free_all_bootmem() calls __free_pages_memory(), the
>number of contiguous pages that __free_pages_memory() passes to the
>buddy allocator is limited to BITS_PER_LONG.  BITS_PER_LONG was originally
>chosen to keep things similar to mm/nobootmem.c.  But it is more
>efficient to limit it to MAX_ORDER.
>
>       base   new  change
>8TB    202s  172s   30s
>16TB   401s  351s   50s
>
>That is around 1%-3% improvement on total boot time.
>
>This patch was spun off from the boot time rfc Robin and I had been
>working on.
>
>Signed-off-by: Robin Holt <robin.m.holt@gmail.com>
>Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
>To: "H. Peter Anvin" <hpa@zytor.com>
>To: Ingo Molnar <mingo@kernel.org>
>Cc: Linux Kernel <linux-kernel@vger.kernel.org>
>Cc: Linux MM <linux-mm@kvack.org>
>Cc: Rob Landley <rob@landley.net>
>Cc: Mike Travis <travis@sgi.com>
>Cc: Daniel J Blueman <daniel@numascale-asia.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Greg KH <gregkh@linuxfoundation.org>
>Cc: Yinghai Lu <yinghai@kernel.org>
>Cc: Mel Gorman <mgorman@suse.de>

Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>

>---
> mm/nobootmem.c | 25 ++++++++-----------------
> 1 file changed, 8 insertions(+), 17 deletions(-)
>
>diff --git a/mm/nobootmem.c b/mm/nobootmem.c
>index 61107cf..2c254d3 100644
>--- a/mm/nobootmem.c
>+++ b/mm/nobootmem.c
>@@ -82,27 +82,18 @@ void __init free_bootmem_late(unsigned long addr, unsigned long size)
>
> static void __init __free_pages_memory(unsigned long start, unsigned long end)
> {
>-	unsigned long i, start_aligned, end_aligned;
>-	int order = ilog2(BITS_PER_LONG);
>+	int order;
>
>-	start_aligned = (start + (BITS_PER_LONG - 1)) & ~(BITS_PER_LONG - 1);
>-	end_aligned = end & ~(BITS_PER_LONG - 1);
>+	while (start < end) {
>+		order = min(MAX_ORDER - 1UL, __ffs(start));
>
>-	if (end_aligned <= start_aligned) {
>-		for (i = start; i < end; i++)
>-			__free_pages_bootmem(pfn_to_page(i), 0);
>+		while (start + (1UL << order) > end)
>+			order--;
>
>-		return;
>-	}
>-
>-	for (i = start; i < start_aligned; i++)
>-		__free_pages_bootmem(pfn_to_page(i), 0);
>+		__free_pages_bootmem(pfn_to_page(start), order);
>
>-	for (i = start_aligned; i < end_aligned; i += BITS_PER_LONG)
>-		__free_pages_bootmem(pfn_to_page(i), order);
>-
>-	for (i = end_aligned; i < end; i++)
>-		__free_pages_bootmem(pfn_to_page(i), 0);
>+		start += (1UL << order);
>+	}
> }
>
> static unsigned long __init __free_memory_core(phys_addr_t start,
>-- 
>1.8.2.1
>
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