Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934753Ab3DOJOT (ORCPT ); Mon, 15 Apr 2013 05:14:19 -0400 Received: from smtp.eu.citrix.com ([46.33.159.39]:8206 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934370Ab3DOJOS (ORCPT ); Mon, 15 Apr 2013 05:14:18 -0400 X-IronPort-AV: E=Sophos;i="4.87,474,1363132800"; d="scan'208";a="3550091" Message-ID: <516BC4F5.10307@citrix.com> Date: Mon, 15 Apr 2013 11:14:29 +0200 From: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: "linux-kernel@vger.kernel.org" , "xen-devel@lists.xen.org" Subject: Re: [PATCH v1 2/7] xen-blkback: use balloon pages for all mappings References: <1364382643-3711-1-git-send-email-roger.pau@citrix.com> <1364382643-3711-3-git-send-email-roger.pau@citrix.com> <20130409144733.GA3158@phenom.dumpdata.com> In-Reply-To: <20130409144733.GA3158@phenom.dumpdata.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5748 Lines: 128 On 09/04/13 16:47, Konrad Rzeszutek Wilk wrote: > On Wed, Mar 27, 2013 at 12:10:38PM +0100, Roger Pau Monne wrote: >> Using balloon pages for all granted pages allows us to simplify the >> logic in blkback, especially in the xen_blkbk_map function, since now >> we can decide if we want to map a grant persistently or not after we >> have actually mapped it. This could not be done before because >> persistent grants used ballooned pages, whereas non-persistent grants >> used pages from the kernel. >> >> This patch also introduces several changes, the first one is that the >> list of free pages is no longer global, now each blkback instance has >> it's own list of free pages that can be used to map grants. Also, a >> run time parameter (max_buffer_pages) has been added in order to tune >> the maximum number of free pages each blkback instance will keep in >> it's buffer. >> >> Signed-off-by: Roger Pau Monn? >> Cc: xen-devel@lists.xen.org >> Cc: Konrad Rzeszutek Wilk > > Sorry for the late review. Some comments. >> --- >> Changes since RFC: >> * Fix typos in commit message. >> * Minor fixes in code. >> --- >> Documentation/ABI/stable/sysfs-bus-xen-backend | 8 + >> drivers/block/xen-blkback/blkback.c | 265 +++++++++++++----------- >> drivers/block/xen-blkback/common.h | 5 + >> drivers/block/xen-blkback/xenbus.c | 3 + >> 4 files changed, 165 insertions(+), 116 deletions(-) >> >> diff --git a/Documentation/ABI/stable/sysfs-bus-xen-backend b/Documentation/ABI/stable/sysfs-bus-xen-backend >> index 3d5951c..e04afe0 100644 >> --- a/Documentation/ABI/stable/sysfs-bus-xen-backend >> +++ b/Documentation/ABI/stable/sysfs-bus-xen-backend >> @@ -73,3 +73,11 @@ KernelVersion: 3.0 >> Contact: Konrad Rzeszutek Wilk >> Description: >> Number of sectors written by the frontend. >> + >> +What: /sys/module/xen_blkback/parameters/max_buffer_pages >> +Date: March 2013 >> +KernelVersion: 3.10 >> +Contact: Roger Pau Monn? >> +Description: >> + Maximum number of free pages to keep in each block >> + backend buffer. >> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c >> index f7526db..8a1892a 100644 >> --- a/drivers/block/xen-blkback/blkback.c >> +++ b/drivers/block/xen-blkback/blkback.c >> @@ -63,6 +63,21 @@ static int xen_blkif_reqs = 64; >> module_param_named(reqs, xen_blkif_reqs, int, 0); >> MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate"); >> >> +/* >> + * Maximum number of unused free pages to keep in the internal buffer. >> + * Setting this to a value too low will reduce memory used in each backend, >> + * but can have a performance penalty. >> + * >> + * A sane value is xen_blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST, but can >> + * be set to a lower value that might degrade performance on some intensive >> + * IO workloads. >> + */ >> + >> +static int xen_blkif_max_buffer_pages = 704; >> +module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644); >> +MODULE_PARM_DESC(max_buffer_pages, >> +"Maximum number of free pages to keep in each block backend buffer"); >> + >> /* Run-time switchable: /sys/module/blkback/parameters/ */ >> static unsigned int log_stats; >> module_param(log_stats, int, 0644); >> @@ -82,10 +97,14 @@ struct pending_req { >> int status; >> struct list_head free_list; >> DECLARE_BITMAP(unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST); >> + struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST]; >> }; >> >> #define BLKBACK_INVALID_HANDLE (~0) >> >> +/* Number of free pages to remove on each call to free_xenballooned_pages */ >> +#define NUM_BATCH_FREE_PAGES 10 >> + >> struct xen_blkbk { >> struct pending_req *pending_reqs; >> /* List of all 'pending_req' available */ >> @@ -93,8 +112,6 @@ struct xen_blkbk { >> /* And its spinlock. */ >> spinlock_t pending_free_lock; >> wait_queue_head_t pending_free_wq; >> - /* The list of all pages that are available. */ >> - struct page **pending_pages; >> /* And the grant handles that are available. */ >> grant_handle_t *pending_grant_handles; >> }; >> @@ -143,14 +160,66 @@ static inline int vaddr_pagenr(struct pending_req *req, int seg) >> BLKIF_MAX_SEGMENTS_PER_REQUEST + seg; >> } >> >> -#define pending_page(req, seg) pending_pages[vaddr_pagenr(req, seg)] >> +static inline int get_free_page(struct xen_blkif *blkif, struct page **page) >> +{ >> + unsigned long flags; >> + >> + spin_lock_irqsave(&blkif->free_pages_lock, flags); > > I am curious to why you need to use the irqsave variant one here, as >> + if (list_empty(&blkif->free_pages)) { >> + BUG_ON(blkif->free_pages_num != 0); >> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags); >> + return alloc_xenballooned_pages(1, page, false); > > This function is using an mutex. > > which would imply it is OK to have an non-irq variant of spinlock? Sorry, the previous response is wrong, I need to use irqsave in order to disable interrupts, since put_free_pages is called from interrupt context and it could create a race if for example, put_free_pages is called while we are inside shrink_free_pagepool. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/