linux-kernel - Re: [PATCH vfs 1/2] lib: implement ptrset

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Message-ID: <20141114131202.GB21209@htj.dyndns.org>
Date:	Fri, 14 Nov 2014 08:12:02 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH vfs 1/2] lib: implement ptrset

Hello, Andrew.

On Thu, Nov 13, 2014 at 02:40:41PM -0800, Andrew Morton wrote:
> In that case tjpointer_add() would need to do a kmalloc() for each inode
> which is added to the bdev/cdev, just as ptrset_add() is doing.
> 
> That might require a nasty preload thing.  But really, for just two
> known callers it would be better to require the caller to create the
> storage.
> 
> 
> 	struct tjpointer *new_tpj;
> 
> 	new_tpj = kmalloc(...);
> 	lock();
> 	tjpointer_add(&my_tjp_list, new_tjp, my_pointer);
> 	unlock();
> 
> Basically what I'm saying is nuke the rbtree and use lists.

Hah?  Then, each removal would be O(N) where N is the number of total
block devices and there are cases where massive number of block
devices exist and many are added / removed back-to-back.  I don't
think making those operations O(N^2) is a good idea.

Thanks.

-- 
tejun
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