From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Matt Fleming <matt@console-pimps.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC][PATCH 2/3] track numbers of pagetable pages
Date: Mon, 18 Apr 2011 08:02:04 -0700 [thread overview]
Message-ID: <1303138924.9615.2487.camel@nimitz> (raw)
In-Reply-To: <20110416104456.3915b7de@mfleming-mobl1.ger.corp.intel.com>
On Sat, 2011-04-16 at 10:44 +0100, Matt Fleming wrote:
> > static inline void pgtable_page_dtor(struct mm_struct *mm, struct page *page)
> > {
> > pte_lock_deinit(page);
> > + dec_mm_counter(mm, MM_PTEPAGES);
> > dec_zone_page_state(page, NR_PAGETABLE);
> > }
>
> I'm probably missing something really obvious but...
>
> Is this safe in the non-USE_SPLIT_PTLOCKS case? If we're not using
> split-ptlocks then inc/dec_mm_counter() are only safe when done under
> mm->page_table_lock, right? But it looks to me like we can end up doing,
>
> __pte_alloc()
> pte_alloc_one()
> pgtable_page_ctor()
>
> before acquiring mm->page_table_lock in __pte_alloc().
No, it's probably not safe. We'll have to come up with something a bit
different in that case. Either that, or just kill the non-atomic case.
Surely there's some percpu magic counter somewhere in the kernel that is
optimized for fast (unlocked?) updates and rare, slow reads.
-- Dave
WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Matt Fleming <matt@console-pimps.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC][PATCH 2/3] track numbers of pagetable pages
Date: Mon, 18 Apr 2011 08:02:04 -0700 [thread overview]
Message-ID: <1303138924.9615.2487.camel@nimitz> (raw)
In-Reply-To: <20110416104456.3915b7de@mfleming-mobl1.ger.corp.intel.com>
On Sat, 2011-04-16 at 10:44 +0100, Matt Fleming wrote:
> > static inline void pgtable_page_dtor(struct mm_struct *mm, struct page *page)
> > {
> > pte_lock_deinit(page);
> > + dec_mm_counter(mm, MM_PTEPAGES);
> > dec_zone_page_state(page, NR_PAGETABLE);
> > }
>
> I'm probably missing something really obvious but...
>
> Is this safe in the non-USE_SPLIT_PTLOCKS case? If we're not using
> split-ptlocks then inc/dec_mm_counter() are only safe when done under
> mm->page_table_lock, right? But it looks to me like we can end up doing,
>
> __pte_alloc()
> pte_alloc_one()
> pgtable_page_ctor()
>
> before acquiring mm->page_table_lock in __pte_alloc().
No, it's probably not safe. We'll have to come up with something a bit
different in that case. Either that, or just kill the non-atomic case.
Surely there's some percpu magic counter somewhere in the kernel that is
optimized for fast (unlocked?) updates and rare, slow reads.
-- Dave
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next prev parent reply other threads:[~2011-04-18 15:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-15 17:38 [RFC][PATCH 0/3] track pte pages and use in OOM score Dave Hansen
2011-04-15 17:38 ` Dave Hansen
2011-04-15 17:38 ` [RFC][PATCH 1/3] pass mm in to pgtable ctor/dtor Dave Hansen
2011-04-15 17:38 ` Dave Hansen
2011-04-15 17:38 ` [RFC][PATCH 2/3] track numbers of pagetable pages Dave Hansen
2011-04-15 17:38 ` Dave Hansen
2011-04-16 9:44 ` Matt Fleming
2011-04-16 9:44 ` Matt Fleming
2011-04-18 15:02 ` Dave Hansen [this message]
2011-04-18 15:02 ` Dave Hansen
2011-04-26 14:57 ` Matt Fleming
2011-04-26 14:57 ` Matt Fleming
2011-04-26 19:26 ` Hugh Dickins
2011-04-26 19:26 ` Hugh Dickins
2011-04-15 17:38 ` [RFC][PATCH 3/3] use pte pages in OOM score Dave Hansen
2011-04-15 17:38 ` Dave Hansen
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