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From: David Howells <dhowells@redhat.com>
To: Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@lst.de>,
	linux-mm@kvack.org, linux-cachefs@redhat.com,
	linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, dhowells@redhat.com,
	Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
	linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
	ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v5 04/28] mm: Implement readahead_control pageset expansion
Date: Tue, 23 Mar 2021 22:18:14 +0000	[thread overview]
Message-ID: <161653789422.2770958.2108046612147345000.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk>

Provide a function, readahead_expand(), that expands the set of pages
specified by a readahead_control object to encompass a revised area with a
proposed size and length.

The proposed area must include all of the old area and may be expanded yet
more by this function so that the edges align on (transparent huge) page
boundaries as allocated.

The expansion will be cut short if a page already exists in either of the
areas being expanded into.  Note that any expansion made in such a case is
not rolled back.

This will be used by fscache so that reads can be expanded to cache granule
boundaries, thereby allowing whole granules to be stored in the cache, but
there are other potential users also.

Changes:
- Moved the declaration of readahead_expand() to a better place[1].

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox (Oracle) <willy@infradead.org>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@lst.de>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20210217161358.GM2858050@casper.infradead.org/ [1]
Link: https://lore.kernel.org/r/159974633888.2094769.8326206446358128373.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/160588479816.3465195.553952688795241765.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118131787.1232039.4863969952441067985.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161028670.2537118.13831420617039766044.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340389201.1303470.14353807284546854878.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539530488.286939.18085961677838089157.stgit@warthog.procyon.org.uk/ # v4
---

 include/linux/pagemap.h |    2 +
 mm/readahead.c          |   70 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index da5c38864037..5c14a9365aae 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -837,6 +837,8 @@ void page_cache_sync_ra(struct readahead_control *, struct file_ra_state *,
 		unsigned long req_count);
 void page_cache_async_ra(struct readahead_control *, struct file_ra_state *,
 		struct page *, unsigned long req_count);
+void readahead_expand(struct readahead_control *ractl,
+		      loff_t new_start, size_t new_len);
 
 /**
  * page_cache_sync_readahead - generic file readahead
diff --git a/mm/readahead.c b/mm/readahead.c
index c5b0457415be..4446dada0bc2 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -638,3 +638,73 @@ SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
 {
 	return ksys_readahead(fd, offset, count);
 }
+
+/**
+ * readahead_expand - Expand a readahead request
+ * @ractl: The request to be expanded
+ * @new_start: The revised start
+ * @new_len: The revised size of the request
+ *
+ * Attempt to expand a readahead request outwards from the current size to the
+ * specified size by inserting locked pages before and after the current window
+ * to increase the size to the new window.  This may involve the insertion of
+ * THPs, in which case the window may get expanded even beyond what was
+ * requested.
+ *
+ * The algorithm will stop if it encounters a conflicting page already in the
+ * pagecache and leave a smaller expansion than requested.
+ *
+ * The caller must check for this by examining the revised @ractl object for a
+ * different expansion than was requested.
+ */
+void readahead_expand(struct readahead_control *ractl,
+		      loff_t new_start, size_t new_len)
+{
+	struct address_space *mapping = ractl->mapping;
+	pgoff_t new_index, new_nr_pages;
+	gfp_t gfp_mask = readahead_gfp_mask(mapping);
+
+	new_index = new_start / PAGE_SIZE;
+
+	/* Expand the leading edge downwards */
+	while (ractl->_index > new_index) {
+		unsigned long index = ractl->_index - 1;
+		struct page *page = xa_load(&mapping->i_pages, index);
+
+		if (page && !xa_is_value(page))
+			return; /* Page apparently present */
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return;
+		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
+			put_page(page);
+			return;
+		}
+
+		ractl->_nr_pages++;
+		ractl->_index = page->index;
+	}
+
+	new_len += new_start - readahead_pos(ractl);
+	new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE);
+
+	/* Expand the trailing edge upwards */
+	while (ractl->_nr_pages < new_nr_pages) {
+		unsigned long index = ractl->_index + ractl->_nr_pages;
+		struct page *page = xa_load(&mapping->i_pages, index);
+
+		if (page && !xa_is_value(page))
+			return; /* Page apparently present */
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return;
+		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
+			put_page(page);
+			return;
+		}
+		ractl->_nr_pages++;
+	}
+}
+EXPORT_SYMBOL(readahead_expand);



  parent reply	other threads:[~2021-03-23 22:19 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23 22:17 [PATCH v5 00/28] Network fs helper library & fscache kiocb API David Howells
2021-03-23 22:17 ` [PATCH v5 01/28] iov_iter: Add ITER_XARRAY David Howells
2021-03-23 22:17 ` [PATCH v5 02/28] mm: Add wait_on_page_writeback_killable() David Howells
2021-03-23 22:18 ` [PATCH v5 03/28] mm: Add set/end/wait functions for PG_private_2 David Howells
2021-03-23 22:18 ` David Howells [this message]
2021-03-23 22:18 ` [PATCH v5 05/28] netfs: Make a netfs helper module David Howells
2021-03-23 22:18 ` [PATCH v5 06/28] netfs: Documentation for helper library David Howells
2021-03-23 22:18 ` [PATCH v5 07/28] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-03-23 22:18 ` [PATCH v5 08/28] netfs, mm: Add set/end/wait_on_page_fscache() aliases David Howells
2021-03-23 22:19 ` [PATCH v5 09/28] netfs: Provide readahead and readpage netfs helpers David Howells
2021-03-23 22:19 ` [PATCH v5 10/28] netfs: Add tracepoints David Howells
2021-03-23 22:19 ` [PATCH v5 11/28] netfs: Gather stats David Howells
2021-03-23 22:19 ` [PATCH v5 12/28] netfs: Add write_begin helper David Howells
2021-03-23 22:19 ` [PATCH v5 13/28] netfs: Define an interface to talk to a cache David Howells
2021-03-23 22:20 ` [PATCH v5 14/28] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-03-23 22:20 ` [PATCH v5 15/28] afs: Disable use of the fscache I/O routines David Howells
2021-03-23 22:20 ` [PATCH v5 16/28] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-03-23 22:20 ` [PATCH v5 17/28] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-03-23 22:21 ` [PATCH v5 18/28] afs: Move key to afs_read struct David Howells
2021-03-23 22:21 ` [PATCH v5 19/28] afs: Don't truncate iter during data fetch David Howells
2021-03-23 22:21 ` [PATCH v5 20/28] afs: Log remote unmarshalling errors David Howells
2021-03-23 22:21 ` [PATCH v5 21/28] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-03-23 22:21 ` [PATCH v5 22/28] afs: Use ITER_XARRAY for writing David Howells
2021-03-23 22:22 ` [PATCH v5 23/28] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-03-23 22:22 ` [PATCH v5 24/28] afs: Extract writeback extension into its own function David Howells
2021-03-23 22:22 ` [PATCH v5 25/28] afs: Prepare for use of THPs David Howells
2021-03-23 22:22 ` [PATCH v5 26/28] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-03-23 22:22 ` [PATCH v5 27/28] afs: Use new fscache read helper API David Howells
2021-03-23 22:23 ` [PATCH v5 28/28] afs: Use the fscache_write_begin() helper David Howells

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