linux-kernel - Re: [PATCH v3 3/7] mm: add find_get_entries

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Date:	Thu, 10 Dec 2015 12:31:53 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dan Williams <dan.j.williams@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Dave Chinner <david@...morbit.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-mm <linux-mm@...ck.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	ext4 hackers <linux-ext4@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>
Subject: Re: [PATCH v3 3/7] mm: add find_get_entries_tag()

On Thu, Dec 10, 2015 at 12:24 PM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> On Wed, Dec 09, 2015 at 11:44:16AM -0800, Dan Williams wrote:
>> On Tue, Dec 8, 2015 at 11:18 AM, Ross Zwisler
>> <ross.zwisler@...ux.intel.com> wrote:
>> > Add find_get_entries_tag() to the family of functions that include
>> > find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
>> > needed for DAX dirty page handling because we need a list of both page
>> > offsets and radix tree entries ('indices' and 'entries' in this function)
>> > that are marked with the PAGECACHE_TAG_TOWRITE tag.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> <>
>> Why does this mostly duplicate find_get_entries()?
>>
>> Surely find_get_entries() can be implemented as a special case of
>> find_get_entries_tag().
>
> I'm adding find_get_entries_tag() to the family of functions that already
> exist and include find_get_entries(), find_get_pages(),
> find_get_pages_contig() and find_get_pages_tag().
>
> These functions all contain very similar code with small changes to the
> internal looping based on whether you're looking through all radix slots or
> only the ones that match a certain tag (radix_tree_for_each_slot() vs
> radix_tree_for_each_tagged()).
>
> We already have find_get_page() to get all pages in a range and
> find_get_pages_tag() to get all pages in the range with a certain tag.  We
> have find_get_entries() to get all pages and indices for a given range, but we
> are currently missing find_get_entries_tag() to do that same search based on a
> tag, which is what I'm adding.
>
> I agree that we could probably figure out a way to combine the code for
> find_get_entries() with find_get_entries_tag(), as we could do for the
> existing functions find_get_pages() and find_get_pages_tag().  I think we
> should probably add find_get_entries_tag() per this patch, though, and then
> decide whether to do any combining later as a separate step.

Ok, sounds good to me.
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