From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [RFC 0/3] Add madvise(..., MADV_WILLWRITE) Date: Wed, 07 Aug 2013 10:40:52 -0700 Message-ID: <520286A4.1020101@intel.com> References: <20130807134058.GC12843@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andy Lutomirski , linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Jan Kara Return-path: In-Reply-To: <20130807134058.GC12843@quack.suse.cz> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On 08/07/2013 06:40 AM, Jan Kara wrote: > One question before I look at the patches: Why don't you use fallocate() > in your application? The functionality you require seems to be pretty > similar to it - writing to an already allocated block is usually quick. One problem I've seen is that it still costs you a fault per-page to get the PTEs in to a state where you can write to the memory. MADV_WILLNEED will do readahead to get the page cache filled, but it still leaves the pages unmapped. Those faults get expensive when you're trying to do a couple hundred million of them all at once. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org