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

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Date:	Fri, 18 Dec 2015 10:33:23 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Theodore Ts'o <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-nvdimm@...ts.01.org, x86@...nel.org,
	xfs@....sgi.com, Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 3/7] mm: add find_get_entries_tag()

On Tue 08-12-15 12:18:41, Ross Zwisler 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>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

But I agree with Daniel that some refactoring to remove common code would
be good.

								Honza

> ---
>  include/linux/pagemap.h |  3 +++
>  mm/filemap.c            | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 71 insertions(+)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 26eabf5..4db0425 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -361,6 +361,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
>  			       unsigned int nr_pages, struct page **pages);
>  unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
>  			int tag, unsigned int nr_pages, struct page **pages);
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> +			int tag, unsigned int nr_entries,
> +			struct page **entries, pgoff_t *indices);
>  
>  struct page *grab_cache_page_write_begin(struct address_space *mapping,
>  			pgoff_t index, unsigned flags);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 167a4d9..99dfbc9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1498,6 +1498,74 @@ repeat:
>  }
>  EXPORT_SYMBOL(find_get_pages_tag);
>  
> +/**
> + * find_get_entries_tag - find and return entries that match @tag
> + * @mapping:	the address_space to search
> + * @start:	the starting page cache index
> + * @tag:	the tag index
> + * @nr_entries:	the maximum number of entries
> + * @entries:	where the resulting entries are placed
> + * @indices:	the cache indices corresponding to the entries in @entries
> + *
> + * Like find_get_entries, except we only return entries which are tagged with
> + * @tag.
> + */
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> +			int tag, unsigned int nr_entries,
> +			struct page **entries, pgoff_t *indices)
> +{
> +	void **slot;
> +	unsigned int ret = 0;
> +	struct radix_tree_iter iter;
> +
> +	if (!nr_entries)
> +		return 0;
> +
> +	rcu_read_lock();
> +restart:
> +	radix_tree_for_each_tagged(slot, &mapping->page_tree,
> +				   &iter, start, tag) {
> +		struct page *page;
> +repeat:
> +		page = radix_tree_deref_slot(slot);
> +		if (unlikely(!page))
> +			continue;
> +		if (radix_tree_exception(page)) {
> +			if (radix_tree_deref_retry(page)) {
> +				/*
> +				 * Transient condition which can only trigger
> +				 * when entry at index 0 moves out of or back
> +				 * to root: none yet gotten, safe to restart.
> +				 */
> +				goto restart;
> +			}
> +
> +			/*
> +			 * A shadow entry of a recently evicted page, a swap
> +			 * entry from shmem/tmpfs or a DAX entry.  Return it
> +			 * without attempting to raise page count.
> +			 */
> +			goto export;
> +		}
> +		if (!page_cache_get_speculative(page))
> +			goto repeat;
> +
> +		/* Has the page moved? */
> +		if (unlikely(page != *slot)) {
> +			page_cache_release(page);
> +			goto repeat;
> +		}
> +export:
> +		indices[ret] = iter.index;
> +		entries[ret] = page;
> +		if (++ret == nr_entries)
> +			break;
> +	}
> +	rcu_read_unlock();
> +	return ret;
> +}
> +EXPORT_SYMBOL(find_get_entries_tag);
> +
>  /*
>   * CD/DVDs are error prone. When a medium error occurs, the driver may fail
>   * a _large_ part of the i/o request. Imagine the worst scenario:
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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