linux-kernel - Re: [PATCH] memblock: Don't adjust size in memblock_find

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Message-ID: <4D2D056B.6050006@kernel.org>
Date:	Tue, 11 Jan 2011 17:35:39 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	David Miller <davem@...emloft.net>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memblock: Don't adjust size in memblock_find_base()

On 01/09/2011 09:56 PM, Benjamin Herrenschmidt wrote:
> On Fri, 2011-01-07 at 12:41 -0800, Yinghai Lu wrote:
>> While applying patch to use memblock to find aperture for 64bit x86.
>> Ingo found system with 1g + force_iommu
> 
> Please run that through DaveM. I seem to remember that he relies on the
> size alignment to ensure that a lot of tiny allocations get properly
> coalesced or he runs out of regions at boot time.

David, can you check this patch on sparc?

[PATCH] memblock: Don't adjust size in memblock_find_base()

While applying patch to use memblock to find aperture for 64bit x86.
Ingo found system with 1g + force_iommu

> No AGP bridge found
> Node 0: aperture @ 38000000 size 32 MB
> Aperture pointing to e820 RAM. Ignoring.
> Your BIOS doesn't leave a aperture memory hole
> Please enable the IOMMU option in the BIOS setup
> This costs you 64 MB of RAM
> Cannot allocate aperture memory hole (0,65536K)

the corresponding code:
	addr = memblock_find_in_range(0, 1ULL<<32, aper_size, 512ULL<<20);
	if (addr == MEMBLOCK_ERROR || addr + aper_size > 0xffffffff) {
		printk(KERN_ERR
			"Cannot allocate aperture memory hole (%lx,%uK)\n",
				addr, aper_size>>10);
		return 0;
	}
	memblock_x86_reserve_range(addr, addr + aper_size, "aperture64")

it failes because memblock core code align the size with 512M. that could make
size way too big.

So don't align the size in that case.

acctually __memblock_alloc_base, the another caller already align that before calling that function.

BTW. x86 does not use __memblock_alloc_base...

Signed-off-by: Yinghai Lu <yinghai@...nel.org>

---
 mm/memblock.c |    2 --
 1 file changed, 2 deletions(-)

Index: linux-2.6/mm/memblock.c
===================================================================
--- linux-2.6.orig/mm/memblock.c
+++ linux-2.6/mm/memblock.c
@@ -137,8 +137,6 @@ static phys_addr_t __init_memblock membl
 
 	BUG_ON(0 == size);
 
-	size = memblock_align_up(size, align);
-
 	/* Pump up max_addr */
 	if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
 		end = memblock.current_limit;
--
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