From mboxrd@z Thu Jan  1 00:00:00 1970
From: Azat Khuzhin <a3at.mail@gmail.com>
Subject: Re: [PATCH vfs 1/2] lib: implement ptrset
Date: Tue, 18 Nov 2014 18:56:29 +0300
Message-ID: <20141118155629.GV10766@azat>
References: <20141113220927.GF2598@htj.dyndns.org>
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Cc: Jens Axboe <axboe@kernel.dk>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
To: Tejun Heo <tj@kernel.org>
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On Thu, Nov 13, 2014 at 05:09:27PM -0500, Tejun Heo wrote:
> +int ptrset_add(void *ptr, struct ptrset *set, gfp_t gfp)
> +{
> +	struct ptrset_elem *elem;
> +	struct rb_node *parent, **slot;
> +
> +	elem = kmalloc(sizeof(*elem), gfp);
> +	if (!elem && !in_interrupt())	/* see ptrset_preload() */
> +		elem = this_cpu_xchg(ptrset_preload_elem, NULL);
> +	if (!elem)
> +		return -ENOMEM;
> +	elem->ptr = ptr;
> +
> +	if (ptrset_find_slot(elem->ptr, set, &slot, &parent)) {
> +		kfree(elem);
> +		return -EEXIST;
> +	}

Maybe allocation *after* ptrset_find_slot() will be better?
This will avoid extra kmalloc/kfree if such ptr already exist (and also
will avoid ENOMEM for such cases).