linux-kernel - Re: [PATCH V3 02/12] kernfs: implement i

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Date:   Mon, 19 Jun 2017 14:52:18 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Shaohua Li <shli@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        gregkh@...uxfoundation.org, hch@....de, axboe@...com,
        rostedt@...dmis.org, lizefan@...wei.com, Kernel-team@...com,
        Shaohua Li <shli@...com>
Subject: Re: [PATCH V3 02/12] kernfs: implement i_generation

On Thu, Jun 15, 2017 at 11:17:10AM -0700, Shaohua Li wrote:
> From: Shaohua Li <shli@...com>
> 
> Set i_generation for kernfs inode. This is required to implement
> exportfs operations. The generation is 32-bit, so it's possible the
> generation wraps up and we find stale files. To reduce the posssibility,
> we don't reuse inode numer immediately. When the inode number allocation
> wraps, we increase generation number. In this way generation/inode
> number consist of a 64-bit number which is unlikely duplicated. This
> does make the idr tree more sparse and waste some memory. Since idr
> manages 32-bit keys, idr uses a 6-level radix tree, each level covers 6
> bits of the key. In a 100k inode kernfs, the worst case will have around
> 300k radix tree node. Each node is 576bytes, so the tree will use about
> ~150M memory. Sounds not too bad, if this really is a problem, we should
> find better data structure.
> 
> Signed-off-by: Shaohua Li <shli@...com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun