From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Walls Subject: Re: [PATCH 5/5] kfifo: log based kfifo API Date: Tue, 08 Jan 2013 16:10:07 -0500 Message-ID: References: <1357657073-27352-1-git-send-email-yuanhan.liu@linux.intel.com> <1357657073-27352-6-git-send-email-yuanhan.liu@linux.intel.com> <20130108181645.GA7972@core.coreip.homeip.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: linux-kernel@vger.kernel.org, Stefani Seibold , Andrew Morton , linux-omap@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, platform-driver-x86@vger.kernel.org, linux-input@vger.kernel.org, linux-iio@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mtd@lists.infradead.org, libertas-dev@lists.infradead.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, open-iscsi@googlegroups.com, linux-scsi@vger.kernel.org, devel@driverdev.osuosl.org, linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, linux-mm@kvack.org, dccp@vger.kernel.org, linux-sctp@vger.kernel.org To: Dmitry Torokhov , Yuanhan Liu Return-path: In-Reply-To: <20130108181645.GA7972@core.coreip.homeip.net> Sender: owner-linux-mm@kvack.org List-Id: netdev.vger.kernel.org Dmitry Torokhov wrote: >Hi Yuanhan, > >On Tue, Jan 08, 2013 at 10:57:53PM +0800, Yuanhan Liu wrote: >> The current kfifo API take the kfifo size as input, while it rounds >> _down_ the size to power of 2 at __kfifo_alloc. This may introduce >> potential issue. >>=20 >> Take the code at drivers/hid/hid-logitech-dj.c as example: >>=20 >> if (kfifo_alloc(&djrcv_dev->notif_fifo, >> DJ_MAX_NUMBER_NOTIFICATIONS * sizeof(struct >dj_report), >> GFP_KERNEL)) { >>=20 >> Where, DJ_MAX_NUMBER_NOTIFICATIONS is 8, and sizeo of(struct >dj_report) >> is 15. >>=20 >> Which means it wants to allocate a kfifo buffer which can store 8 >> dj_report entries at once. The expected kfifo buffer size would be >> 8 * 15 =3D 120 then. While, in the end, __kfifo_alloc will turn the >> size to rounddown_power_of_2(120) =3D 64, and then allocate a buf >> with 64 bytes, which I don't think this is the original author want. >>=20 >> With the new log API, we can do like following: >>=20 >> int kfifo_size_order =3D order_base_2(DJ_MAX_NUMBER_NOTIFICATIONS * >> sizeof(struct dj_report)); >>=20 >> if (kfifo_alloc(&djrcv_dev->notif_fifo, kfifo_size_order, >GFP_KERNEL)) { >>=20 >> This make sure we will allocate enough kfifo buffer for holding >> DJ_MAX_NUMBER_NOTIFICATIONS dj_report entries. > >Why don't you simply change __kfifo_alloc to round the allocation up >instead of down? > >Thanks. > >--=20 >Dmitry >-- >To unsubscribe from this list: send the line "unsubscribe linux-media" >in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html Hi Dmitry, I agree. I don't see the benefit in pushing up the change to a kfifo in= ternal decision/problem to many different places in the kernel. Regards, Andy =20 -- 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