linux-kernel - Re: [PATCH 17/35] x86, lmb: Add x86 version of __lmb_find

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Message-ID: <4BECF21C.7030006@oracle.com>
Date:	Thu, 13 May 2010 23:47:56 -0700
From:	Yinghai <yinghai.lu@...cle.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 17/35] x86, lmb: Add x86 version of __lmb_find_area()

On 05/13/2010 07:34 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2010-05-13 at 17:19 -0700, Yinghai Lu wrote:
>> Generic version is going from high to low, and it seems it can not find
>> right area compact enough.
>>
>> the x86 version will go from goal to limit and just like the way We used
>> for early_res
>>
>> use ARCH_FIND_LMB_AREA to select from them.
> 
> Why the heck ?
> 
> So LMB is designed to work top->down and now you replace lmb_find_area()
> with a -completely different- implementation that goes bottom->up
> without any explanation as to why you are doing so ?
> 
> top->down tend to be move efficient at keeping things less fragmented
> btw.

for safe, and there is any problem with top to down allocation, we can ask user to check if low to high works...

not just make user to get broken kernel.

> 
> Cheers,
> Ben.
> 
>> -v2: default to no
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>> ---
>>  arch/x86/Kconfig  |    8 +++++
>>  arch/x86/mm/lmb.c |   78 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 86 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index d80d2ab..36a5665 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -584,6 +584,14 @@ config PARAVIRT_DEBUG
>>  	  Enable to debug paravirt_ops internals.  Specifically, BUG if
>>  	  a paravirt_op is missing when it is called.
>>  
>> +config ARCH_LMB_FIND_AREA
>> +	default n
>> +	bool "Use x86 own lmb_find_area()"
>> +	---help---
>> +	  Use lmb_find_area() version instead of generic version, it get free
>> +	  area up from low.
>> +	  Generic one try to get free area down from limit.
>> +
>>  config NO_BOOTMEM
>>  	default y
>>  	bool "Disable Bootmem code"
>> diff --git a/arch/x86/mm/lmb.c b/arch/x86/mm/lmb.c
>> index c0c4220..cf9d488 100644
>> --- a/arch/x86/mm/lmb.c
>> +++ b/arch/x86/mm/lmb.c
>> @@ -435,3 +435,81 @@ u64 __init lmb_hole_size(u64 start, u64 end)
>>  	return end - start - ((u64)ram << PAGE_SHIFT);
>>  }
>>  
>> +#ifdef CONFIG_ARCH_LMB_FIND_AREA
>> +static int __init find_overlapped_early(u64 start, u64 end)
>> +{
>> +	int i;
>> +	struct lmb_region *r;
>> +
>> +	for (i = 0; i < lmb.reserved.cnt && lmb.reserved.regions[i].size; i++) {
>> +		r = &lmb.reserved.regions[i];
>> +		if (end > r->base && start < (r->base + r->size))
>> +			break;
>> +	}
>> +
>> +	return i;
>> +}
>> +
>> +/* Check for already reserved areas */
>> +static inline bool __init bad_addr(u64 *addrp, u64 size, u64 align)
>> +{
>> +	int i;
>> +	u64 addr = *addrp;
>> +	bool changed = false;
>> +	struct lmb_region *r;
>> +again:
>> +	i = find_overlapped_early(addr, addr + size);
>> +	r = &lmb.reserved.regions[i];
>> +	if (i < lmb.reserved.cnt && r->size) {
>> +		*addrp = addr = round_up(r->base + r->size, align);
>> +		changed = true;
>> +		goto again;
>> +	}
>> +	return changed;
>> +}
>> +
>> +u64 __init __lmb_find_area(u64 ei_start, u64 ei_last, u64 start, u64 end,
>> +				 u64 size, u64 align)
>> +{
>> +	u64 addr, last;
>> +
>> +	addr = round_up(ei_start, align);
>> +	if (addr < start)
>> +		addr = round_up(start, align);
>> +	if (addr >= ei_last)
>> +		goto out;
>> +	while (bad_addr(&addr, size, align) && addr+size <= ei_last)
>> +		;
>> +	last = addr + size;
>> +	if (last > ei_last)
>> +		goto out;
>> +	if (last > end)
>> +		goto out;
>> +
>> +	return addr;
>> +
>> +out:
>> +	return LMB_ERROR;
>> +}
>> +
>> +/*
>> + * Find a free area with specified alignment in a specific range.
>> + */
>> +u64 __init lmb_find_area(u64 start, u64 end, u64 size, u64 align)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < lmb.memory.cnt; i++) {
>> +		u64 ei_start = lmb.memory.regions[i].base;
>> +		u64 ei_last = ei_start + lmb.memory.regions[i].size;
>> +		u64 addr;
>> +
>> +		addr = __lmb_find_area(ei_start, ei_last, start, end,
>> +					 size, align);
>> +
>> +		if (addr != LMB_ERROR)
>> +			return addr;
>> +	}
>> +	return LMB_ERROR;
>> +}
>> +#endif
> 

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