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Message-ID: <492B4C43.8020506@oracle.com>
Date: Mon, 24 Nov 2008 16:52:19 -0800
From: Randy Dunlap <randy.dunlap@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: David Rientjes <rientjes@...gle.com>, peterz@...radead.org,
david@...morbit.com, cl@...ux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: add dirty_background_bytes and dirty_bytes sysctls
Andrew Morton wrote:
> On Sun, 23 Nov 2008 10:55:16 -0800 (PST)
> David Rientjes <rientjes@...gle.com> wrote:
>
>> This change introduces two new sysctls to /proc/sys/vm:
>> dirty_background_bytes and dirty_bytes.
>>
>>
>> ...
>>
>> @@ -365,23 +429,29 @@ void
>> get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
>> unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
>> {
>> - int background_ratio; /* Percentages */
>> - int dirty_ratio;
>> unsigned long background;
>> unsigned long dirty;
>> unsigned long available_memory = determine_dirtyable_memory();
>> struct task_struct *tsk;
>>
>> - dirty_ratio = vm_dirty_ratio;
>> - if (dirty_ratio < 5)
>> - dirty_ratio = 5;
>> + if (vm_dirty_bytes)
>> + dirty = (vm_dirty_bytes + PAGE_SIZE) / PAGE_SIZE;
>
> It would be conventional to use DIV_ROUND_UP() here.
>
>> + else {
>> + int dirty_ratio;
>
> hm, I wonder why vm_dirty_ratio has a signed type.
>
>> - background_ratio = dirty_background_ratio;
>> - if (background_ratio >= dirty_ratio)
>> - background_ratio = dirty_ratio / 2;
>> + dirty_ratio = vm_dirty_ratio;
>> + if (dirty_ratio < 5)
>> + dirty_ratio = 5;
>> + dirty = (dirty_ratio * available_memory) / 100;
>> + }
>> +
>> + if (dirty_background_bytes)
>> + background = (dirty_background_bytes + PAGE_SIZE) / PAGE_SIZE;
>
> DIV_ROUND_UP()?
Note that DIV_ROUND_UP() would make that
background = (dirty_background_byte + PAGE_SIZE - 1) / PAGE_SIZE;
but that's usually what is needed/intended.
>> + else
>> + background = (dirty_background_ratio * available_memory) / 100;
>>
>> - background = (background_ratio * available_memory) / 100;
>> - dirty = (dirty_ratio * available_memory) / 100;
>> + if (background >= dirty)
>> + background = dirty / 2;
>> tsk = current;
>> if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
>> background += background / 4;
--
~Randy
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