From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirill A. Shutemov" Subject: Re: [PATCH v5 03/78] xarray: Add the xa_lock to the radix_tree_root Date: Wed, 27 Dec 2017 13:18:34 +0300 Message-ID: <20171227101834.qfjsy6eqaojiifsr@node.shutemov.name> References: <20171215220450.7899-1-willy@infradead.org> <20171215220450.7899-4-willy@infradead.org> <20171226165440.tv6inwa2fgk3bfy6@node.shutemov.name> <20171227034340.GC24828@bombadil.infradead.org> <20171227035815.GD24828@bombadil.infradead.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=yBfQVT3oFqhNgNRHy/5mlCCHdHfi+E/c/vLmLyhHQOA=; b=M1FDDjv7ElUgqyQzwZi0psofpAFkLiwxtdSlmTbukXxRRijYzF1/TBMOVIkwRxIBdq X4L5xZfY2rP9HS09Ru7nl/U6OJrXmOCQEytzu/6e3tRf52lFhV0vOu7ihMz4p3QPTQTD +5gIHKG2zOfWgoFGaGFFbCTkdI4jDZd2yVR2y7gJHRDdXaCf326sKqpmYt7zwys936rL aYQ99Qauez9Pxv5RZ2IKzJBi68tID8oF0YUO1aNNTEumlELn/I/rcHwyg0yKC9I2kTdH cxthi+tleqzECCL8fHx1mk/I9nIgx0FPvDjZK+GHLUzTWoqFU0C2xS1qkj3xzClM1PMV mVDw== Content-Disposition: inline In-Reply-To: <20171227035815.GD24828@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Matthew Wilcox 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 07:58:15PM -0800, Matthew Wilcox wrote: > 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 Yeah, that's neat. Dealing with old compilers is frustrating... -- Kirill A. Shutemov -- 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