From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 3AC8D6B0033 for ; Tue, 26 Dec 2017 22:58:31 -0500 (EST) Received: by mail-pl0-f69.google.com with SMTP id m39so19454221plg.19 for ; Tue, 26 Dec 2017 19:58:31 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id q12si24084479pls.475.2017.12.26.19.58.30 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 26 Dec 2017 19:58:30 -0800 (PST) Date: Tue, 26 Dec 2017 19:58:15 -0800 From: Matthew Wilcox Subject: Re: [PATCH v5 03/78] xarray: Add the xa_lock to the radix_tree_root Message-ID: <20171227035815.GD24828@bombadil.infradead.org> References: <20171215220450.7899-1-willy@infradead.org> <20171215220450.7899-4-willy@infradead.org> <20171226165440.tv6inwa2fgk3bfy6@node.shutemov.name> <20171227034340.GC24828@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171227034340.GC24828@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: linux-kernel@vger.kernel.org, Matthew Wilcox , Ross Zwisler , David Howells , Shaohua Li , Jens Axboe , Rehas Sachdeva , Marc Zyngier , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-nilfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-usb@vger.kernel.org, linux-raid@vger.kernel.org On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote: > Also add the xa_lock() and xa_unlock() family of wrappers to make it > easier to use the lock. If we could rely on -fplan9-extensions in > the compiler, we could avoid all of this syntactic sugar, but that > wasn't added until gcc 4.6. Oh, in case anyone's wondering, here's how I'd do it with plan9 extensions: struct xarray { spinlock_t; int xa_flags; void *xa_head; }; ... spin_lock_irqsave(&mapping->pages, flags); __delete_from_page_cache(page, NULL); spin_unlock_irqrestore(&mapping->pages, flags); ... The plan9 extensions permit passing a pointer to a struct which has an unnamed element to a function which is expecting a pointer to the type of that element. The compiler does any necessary arithmetic to produce a pointer. It's exactly as if I had written: spin_lock_irqsave(&mapping->pages.xa_lock, flags); __delete_from_page_cache(page, NULL); spin_unlock_irqrestore(&mapping->pages.xa_lock, flags); More details here: https://9p.io/sys/doc/compiler.html -- 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