From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 11 Oct 2016 15:48:17 -0600 From: Ross Zwisler To: Christoph Hellwig Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Theodore Ts'o , Alexander Viro , Andreas Dilger , Andrew Morton , Dan Williams , Dave Chinner , Jan Kara , Matthew Wilcox , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support Message-ID: <20161011214817.GB32165@linux.intel.com> References: <1475874544-24842-1-git-send-email-ross.zwisler@linux.intel.com> <1475874544-24842-16-git-send-email-ross.zwisler@linux.intel.com> <20161010155917.GA19978@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161010155917.GA19978@lst.de> Sender: owner-linux-mm@kvack.org List-ID: On Mon, Oct 10, 2016 at 05:59:17PM +0200, Christoph Hellwig wrote: > On Fri, Oct 07, 2016 at 03:09:02PM -0600, Ross Zwisler wrote: > > - if (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD) > > + if ((unsigned long)entry & RADIX_DAX_PMD) > > Please introduce a proper inline helper that mask all the possible type > bits out of the radix tree entry, and use them wherever you do the > open cast. Yea, this is messy. I tried having temporary flags, but that's basically where we came from with the old 'type' thing which used to be RADIX_DAX_PTE|RADIX_DAX_PMD. After playing with it a bit it seems like the cleanest way is to have a little flag test helper, like this: static int dax_flag_test(void *entry, int flags) { return (unsigned long)entry & flags; } ... /* * Besides huge zero pages the only other thing that gets * downgraded are empty entries which don't need to be * unmapped. */ if (pmd_downgrade && dax_flag_test(entry, RADIX_DAX_HZP)) unmap_mapping_range(mapping, (index << PAGE_SHIFT) & PMD_MASK, PMD_SIZE, 0); etc. Please let me know if this is undesirable for some reason. Vs keeping the flags in a local variable, this is good because a) it doesn't require callers to cast, and b) it makes operator precedence easy because the flags are a param, so no "flags & (flag1|flag2)" nesting, and c) we don't keep a local variable that could get out of sync with 'entry'. > > restart: > > spin_lock_irq(&mapping->tree_lock); > > entry = get_unlocked_mapping_entry(mapping, index, &slot); > > + > > + if (entry) { > > + if (size_flag & RADIX_DAX_PMD) { > > + if (!radix_tree_exceptional_entry(entry) || > > + !((unsigned long)entry & RADIX_DAX_PMD)) { > > + entry = ERR_PTR(-EEXIST); > > + goto out_unlock; > > + } > > + } else { /* trying to grab a PTE entry */ > > + if (radix_tree_exceptional_entry(entry) && > > + ((unsigned long)entry & RADIX_DAX_PMD) && > > + ((unsigned long)entry & > > + (RADIX_DAX_HZP|RADIX_DAX_EMPTY))) { > > And when we do these cases N times next to each other we should > have a local variable the valid flag bits of entry. -- 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