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Date: Wed, 12 Mar 2014 20:03:03 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Jerome Marchand <jmarchan@redhat.com>
Subject: Re: [PATCH v3] zram: support REQ_DISCARD
Message-Id: <20140312200303.7abc49b0.akpm@linux-foundation.org>
In-Reply-To: <20140313024617.GA4900@lge.com>
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On Thu, 13 Mar 2014 11:46:17 +0900 Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:

> +	while (n >= PAGE_SIZE) {
> +		/*
> +		 * discard request can be too large so that the zram can
> +		 * be stucked for a long time if we handle the request
> +		 * at once. So handle the request by PAGE_SIZE unit at a time.
> +		 */
> +		write_lock(&zram->meta->tb_lock);
> +		zram_free_page(zram, index);
> +		write_unlock(&zram->meta->tb_lock);
> +		index++;
> +		n -= PAGE_SIZE;
> +	}

Well, you could use something like

	if (need_resched()) {
		unlock()
		schedule()
		lock()
	}

here, or free 100 pages at a time or something silly like that.  I
guess we retain these as options if/when that lock turns out to be
contended.