From: Jan Kara <jack@suse.cz>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
William Kucharski <william.kucharski@oracle.com>,
Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
Yang Shi <yang.shi@linux.alibaba.com>,
Dave Chinner <dchinner@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 04/12] mm/filemap: Add mapping_seek_hole_data
Date: Tue, 29 Sep 2020 10:46:53 +0200 [thread overview]
Message-ID: <20200929084653.GC10896@quack2.suse.cz> (raw)
In-Reply-To: <20200914130042.11442-5-willy@infradead.org>
On Mon 14-09-20 14:00:34, Matthew Wilcox (Oracle) wrote:
> Rewrite shmem_seek_hole_data() and move it to filemap.c.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
...
> +/**
> + * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
> + * @mapping: Address space to search.
> + * @start: First byte to consider.
> + * @end: Limit of search (exclusive).
> + * @whence: Either SEEK_HOLE or SEEK_DATA.
> + *
> + * If the page cache knows which blocks contain holes and which blocks
> + * contain data, your filesystem can use this function to implement
> + * SEEK_HOLE and SEEK_DATA. This is useful for filesystems which are
> + * entirely memory-based such as tmpfs, and filesystems which support
> + * unwritten extents.
> + *
> + * Return: The requested offset on successs, or -ENXIO if @whence specifies
> + * SEEK_DATA and there is no data after @start. There is an implicit hole
> + * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
> + * and @end contain data.
> + */
> +loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
> + loff_t end, int whence)
> +{
> + XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
> + pgoff_t max = (end - 1) / PAGE_SIZE;
> + bool seek_data = (whence == SEEK_DATA);
> + struct page *page;
> +
> + if (end <= start)
> + return -ENXIO;
> +
> + rcu_read_lock();
> + while ((page = xas_find_get_entry(&xas, max, XA_PRESENT))) {
> + loff_t pos = xas.xa_index * PAGE_SIZE;
OK, but for ordinary filesystems this could be problematic because of
exceptional entries?
Also for shmem you've dropped the PageUptodate check which I'm not sure is
safe?
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-09-29 8:46 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 13:00 [PATCH v2 00/12] Overhaul multi-page lookups for THP Matthew Wilcox (Oracle)
2020-09-14 13:00 ` [PATCH v2 01/12] mm: Make pagecache tagged lookups return only head pages Matthew Wilcox (Oracle)
2020-09-29 9:13 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 02/12] mm/shmem: Use pagevec_lookup in shmem_unlock_mapping Matthew Wilcox (Oracle)
2020-09-29 8:28 ` Jan Kara
2020-09-29 18:36 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 03/12] mm/filemap: Add helper for finding pages Matthew Wilcox (Oracle)
2020-09-29 8:27 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 04/12] mm/filemap: Add mapping_seek_hole_data Matthew Wilcox (Oracle)
2020-09-29 8:46 ` Jan Kara [this message]
2020-09-29 12:42 ` Matthew Wilcox
2020-09-29 13:39 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 05/12] mm: Add and use find_lock_entries Matthew Wilcox (Oracle)
2020-09-29 8:58 ` Jan Kara
2020-09-29 12:48 ` Matthew Wilcox
2020-09-30 10:40 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 06/12] mm: Add an 'end' parameter to find_get_entries Matthew Wilcox (Oracle)
2020-09-14 13:00 ` [PATCH v2 07/12] mm: Add an 'end' parameter to pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:02 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 08/12] mm: Remove nr_entries parameter from pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:03 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 09/12] mm: Pass pvec directly to find_get_entries Matthew Wilcox (Oracle)
2020-09-29 9:07 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 10/12] mm: Remove pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:08 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 11/12] mm/truncate,shmem: Handle truncates that split THPs Matthew Wilcox (Oracle)
2020-09-30 11:59 ` Jan Kara
2020-09-30 14:51 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 12/12] mm/filemap: Return only head pages from find_get_entries Matthew Wilcox (Oracle)
2020-09-30 12:15 ` Jan Kara
2020-09-30 12:36 ` Matthew Wilcox
2020-09-30 17:08 ` Jan Kara
2020-09-30 17:23 ` Matthew Wilcox
2020-10-01 7:17 ` Jan Kara
2020-10-25 23:19 ` Matthew Wilcox
2020-10-26 9:11 ` Jan Kara
2020-09-28 20:13 ` [PATCH v2 00/12] Overhaul multi-page lookups for THP Matthew Wilcox
2020-09-29 8:50 ` William Kucharski
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