From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 7C729900137 for ; Tue, 9 Aug 2011 12:17:09 -0400 (EDT) Message-Id: <4E4179D90200007800050676@nat28.tlf.novell.com> Date: Tue, 09 Aug 2011 17:18:01 +0100 From: "Jan Beulich" Subject: RE: Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes References: <20110808204555.GA15850@ca-server1.us.oracle.com 4E414320020000780005057E@nat28.tlf.novell.com><4E414320020000780005057E@nat28.tlf.novell.com> In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Dan Magenheimer Cc: hannes@cmpxchg.org, jackdachef@gmail.com, hughd@google.com, jeremy@goop.org, npiggin@kernel.dk, linux-mm@kvack.org, akpm@linux-foundation.org, sjenning@linux.vnet.ibm.com, Chris Mason , Konrad Wilk , Kurt Hackel , riel@redhat.com, ngupta@vflare.org, linux-kernel@vger.kernel.org, matthew@wil.cx >>> On 09.08.11 at 17:03, Dan Magenheimer = wrote: >> > --- linux/include/linux/swap.h 2011-08-08 08:19:25.880690134 = -0600 >> > +++ frontswap/include/linux/swap.h 2011-08-08 08:59:03.952691415 = -0600 >> > @@ -194,6 +194,8 @@ struct swap_info_struct { >> > struct block_device *bdev; /* swap device or bdev of swap = file */ >> > struct file *swap_file; /* seldom referenced */ >> > unsigned int old_block_size; /* seldom referenced */ >>=20 >> #ifdef CONFIG_FRONTSWAP >>=20 >> > + unsigned long *frontswap_map; /* frontswap in-use, one bit per = page */ >> > + unsigned int frontswap_pages; /* frontswap pages in-use counter = */ >>=20 >>=20 >> #endif >>=20 >> (to eliminate any overhead with that config option unset) >>=20 >> Jan >=20 > Hi Jan -- >=20 > Thanks for the review! >=20 > As noted in the commit comment, if these structure elements are > not put inside an #ifdef CONFIG_FRONTSWAP, it becomes > unnecessary to clutter the core swap code with several ifdefs. > The cost is one pointer and one unsigned int per allocated > swap device (often no more than one swap device per system), > so the code clarity seemed more important than the tiny > additional runtime space cost. >=20 > Do you disagree? Not necessarily - I just know that in other similar occasions (partly internally to our company) I was asked to make sure turned off features would not leave *any* run time foot print whatsoever. Jan -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org