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Subject: Re: [PATCH] f2fs: introduce nid cache
To: Jaegeuk Kim <jaegeuk@kernel.org>
References: <20170122095331.58427-1-yuchao0@huawei.com>
 <20170124043500.GC1566@jaegeuk.local>
CC: <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
From: Chao Yu <yuchao0@huawei.com>
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Date: Tue, 7 Feb 2017 15:24:05 +0800
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Hi Jaegeuk,

Happy Chinese New Year! :)

On 2017/1/24 12:35, Jaegeuk Kim wrote:
> Hi Chao,
> 
> On 01/22, Chao Yu wrote:
>> In scenario of intensively node allocation, free nids will be ran out
>> soon, then it needs to stop to load free nids by traversing NAT blocks,
>> in worse case, if NAT blocks does not be cached in memory, it generates
>> IOs which slows down our foreground operations.
>>
>> In order to speed up node allocation, in this patch we introduce a new
>> option named "nid cache", when turns on this option, it will load all
>> nat entries in NAT blocks when doing mount, and organize all free nids
>> in a bitmap, for any operations related to free nid, we will query and
>> set the new prebuilded bitmap instead of reading and lookuping NAT
>> blocks, so performance of node allocation can be improved.
>>
> 
> How does this affect mount time and memory consumption?

Sorry for the delay.

Let me figure out some numbers later.

> IMO, if those do not
> raise huge concerns, we would be able to consider just replacing current free
> nid list with this bitmap.

Yup, I agree with you.

Thanks,