linux-kernel - Re: [PATCH] spinlock in function hugetlb

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Message-Id: <1185235388.4688.68.camel@ymzhang>
Date:	Tue, 24 Jul 2007 08:03:08 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Adam Litke <aglitke@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, agl@...ibm.com
Subject: Re: [PATCH] spinlock in function hugetlb_fault could be deleted

On Mon, 2007-07-23 at 09:27 -0500, Adam Litke wrote:
> Hello.  hugetlb_instantiation_mutex is an extremely heavy-weight lock
> whose days are numbered (hopefully).  It exists primarily to arbitrate
> a race condition where n (n > 1) threads of execution race to satisfy
> the same page fault for a process.  Even though only one hugetlb page
> is needed, if (n) are not available, the application can receive a
> bogus VM_FAULT_OOM.
Thanks for your kind comments.

> 
> Anyway, the hugetlb_instantiation_mutex approach has few friends
> around here, so rather than making the code rely more heavily upon it,
> perhaps you could focus you efforts on helping us remove it.
That's the correct direction. I will check if the mutex could be removed. 

> 
> On 7/23/07, Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> > Function hugetlb_fault needn't hold spinlock mm->page_table_lock,
> > because when hugetlb_fault is called:
> > 1) mm->mmap_sem is held already;
> > 2) hugetlb_instantiation_mutex is held by hugetlb_fault, which prevents
> > other threads/processes from entering this critical area. It's impossible
> > for other threads/processes to change the page table now.
> 
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