+ mm-filemap-use-head-pages-in-generic_file_buffered_read.patch added to -mm tree

+ mm-filemap-use-head-pages-in-generic_file_buffered_read.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/filemap: use head pages in generic_file_buffered_read
has been added to the -mm tree.  Its filename is
     mm-filemap-use-head-pages-in-generic_file_buffered_read.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-filemap-use-head-pages-in-generic_file_buffered_read.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-filemap-use-head-pages-in-generic_file_buffered_read.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm/filemap: use head pages in generic_file_buffered_read

Add filemap_get_read_batch() which returns the head pages which represent
a contiguous array of bytes in the file.  It also stops when encountering
a page marked as Readahead or !Uptodate (but does return that page) so it
can be handled appropriately by filemap_get_pages().  That lets us remove
the loop in filemap_get_pages() and check only the last page.

Link: https://lkml.kernel.org/r/20210122160140.223228-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/filemap.c |  122 ++++++++++++++++++++++++++++++++++---------------
 1 file changed, 85 insertions(+), 37 deletions(-)

--- a/mm/filemap.c~mm-filemap-use-head-pages-in-generic_file_buffered_read
+++ a/mm/filemap.c
@@ -2172,6 +2172,51 @@ static int lock_page_for_iocb(struct kio
 		return lock_page_killable(page);
 }
 
+/*
+ * filemap_get_read_batch - Get a batch of pages for read
+ *
+ * Get a batch of pages which represent a contiguous range of bytes
+ * in the file.  No tail pages will be returned.  If @index is in the
+ * middle of a THP, the entire THP will be returned.  The last page in
+ * the batch may have Readahead set or be not Uptodate so that the
+ * caller can take the appropriate action.
+ */
+static void filemap_get_read_batch(struct address_space *mapping,
+		pgoff_t index, pgoff_t max, struct pagevec *pvec)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	struct page *head;
+
+	rcu_read_lock();
+	for (head = xas_load(&xas); head; head = xas_next(&xas)) {
+		if (xas_retry(&xas, head))
+			continue;
+		if (xas.xa_index > max || xa_is_value(head))
+			break;
+		if (!page_cache_get_speculative(head))
+			goto retry;
+
+		/* Has the page moved or been split? */
+		if (unlikely(head != xas_reload(&xas)))
+			goto put_page;
+
+		if (!pagevec_add(pvec, head))
+			break;
+		if (!PageUptodate(head))
+			break;
+		if (PageReadahead(head))
+			break;
+		xas.xa_index = head->index + thp_nr_pages(head) - 1;
+		xas.xa_offset = (xas.xa_index >> xas.xa_shift) & XA_CHUNK_MASK;
+		continue;
+put_page:
+		put_page(head);
+retry:
+		xas_reset(&xas);
+	}
+	rcu_read_unlock();
+}
+
 static struct page *filemap_read_page(struct kiocb *iocb, struct file *filp,
 		struct address_space *mapping, struct page *page)
 {
@@ -2325,15 +2370,15 @@ static int filemap_get_pages(struct kioc
 	struct address_space *mapping = filp->f_mapping;
 	struct file_ra_state *ra = &filp->f_ra;
 	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
-	pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
-	unsigned int nr = min_t(unsigned long, last_index - index, PAGEVEC_SIZE);
-	int i, j, err = 0;
+	pgoff_t last_index;
+	int err = 0;
 
+	last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE);
 find_page:
 	if (fatal_signal_pending(current))
 		return -EINTR;
 
-	pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages);
+	filemap_get_read_batch(mapping, index, last_index, pvec);
 	if (pvec->nr)
 		goto got_pages;
 
@@ -2342,29 +2387,30 @@ find_page:
 
 	page_cache_sync_readahead(mapping, ra, filp, index, last_index - index);
 
-	pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages);
+	filemap_get_read_batch(mapping, index, last_index, pvec);
 	if (pvec->nr)
 		goto got_pages;
 
 	pvec->pages[0] = filemap_create_page(iocb, iter);
 	err = PTR_ERR_OR_ZERO(pvec->pages[0]);
-	if (!IS_ERR_OR_NULL(pvec->pages[0]))
-		pvec->nr = 1;
+	if (IS_ERR_OR_NULL(pvec->pages[0]))
+		goto err;
+	pvec->nr = 1;
+	return 0;
 got_pages:
-	for (i = 0; i < pvec->nr; i++) {
-		struct page *page = pvec->pages[i];
-		pgoff_t pg_index = index + i;
+	{
+		struct page *page = pvec->pages[pvec->nr - 1];
+		pgoff_t pg_index = page->index;
 		loff_t pg_pos = max(iocb->ki_pos,
 				    (loff_t) pg_index << PAGE_SHIFT);
 		loff_t pg_count = iocb->ki_pos + iter->count - pg_pos;
 
 		if (PageReadahead(page)) {
 			if (iocb->ki_flags & IOCB_NOIO) {
-				for (j = i; j < pvec->nr; j++)
-					put_page(pvec->pages[j]);
-				pvec->nr = i;
+				put_page(page);
+				pvec->nr--;
 				err = -EAGAIN;
-				break;
+				goto err;
 			}
 			page_cache_async_readahead(mapping, ra, filp, page,
 					pg_index, last_index - pg_index);
@@ -2372,26 +2418,23 @@ got_pages:
 
 		if (!PageUptodate(page)) {
 			if ((iocb->ki_flags & IOCB_NOWAIT) ||
-			    ((iocb->ki_flags & IOCB_WAITQ) && i)) {
-				for (j = i; j < pvec->nr; j++)
-					put_page(pvec->pages[j]);
-				pvec->nr = i;
+			    ((iocb->ki_flags & IOCB_WAITQ) && pvec->nr > 1)) {
+				put_page(page);
+				pvec->nr--;
 				err = -EAGAIN;
-				break;
+				goto err;
 			}
 
 			page = filemap_update_page(iocb, filp, iter, page,
 					pg_pos, pg_count);
 			if (IS_ERR_OR_NULL(page)) {
-				for (j = i + 1; j < pvec->nr; j++)
-					put_page(pvec->pages[j]);
-				pvec->nr = i;
+				pvec->nr--;
 				err = PTR_ERR_OR_ZERO(page);
-				break;
 			}
 		}
 	}
 
+err:
 	if (likely(pvec->nr))
 		return 0;
 	if (err)
@@ -2436,6 +2479,7 @@ ssize_t generic_file_buffered_read(struc
 		return 0;
 
 	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+	pagevec_init(&pvec);
 
 	do {
 		cond_resched();
@@ -2463,13 +2507,8 @@ ssize_t generic_file_buffered_read(struc
 		isize = i_size_read(inode);
 		if (unlikely(iocb->ki_pos >= isize))
 			goto put_pages;
-
 		end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
 
-		while ((iocb->ki_pos >> PAGE_SHIFT) + pvec.nr >
-		       (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT)
-			put_page(pvec.pages[--pvec.nr]);
-
 		/*
 		 * Once we start copying data, we don't want to be touching any
 		 * cachelines that might be contended:
@@ -2483,24 +2522,32 @@ ssize_t generic_file_buffered_read(struc
 		if (iocb->ki_pos >> PAGE_SHIFT !=
 		    ra->prev_pos >> PAGE_SHIFT)
 			mark_page_accessed(pvec.pages[0]);
-		for (i = 1; i < pagevec_count(&pvec); i++)
-			mark_page_accessed(pvec.pages[i]);
 
 		for (i = 0; i < pagevec_count(&pvec); i++) {
-			unsigned int offset = iocb->ki_pos & ~PAGE_MASK;
-			unsigned int bytes = min_t(loff_t, end_offset - iocb->ki_pos,
-						   PAGE_SIZE - offset);
-			unsigned int copied;
+			struct page *page = pvec.pages[i];
+			size_t page_size = thp_size(page);
+			size_t offset = iocb->ki_pos & (page_size - 1);
+			size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
+					     page_size - offset);
+			size_t copied;
 
+			if (end_offset < page_offset(page))
+				break;
+			if (i > 0)
+				mark_page_accessed(page);
 			/*
 			 * If users can be writing to this page using arbitrary
 			 * virtual addresses, take care about potential aliasing
 			 * before reading the page on the kernel side.
 			 */
-			if (writably_mapped)
-				flush_dcache_page(pvec.pages[i]);
+			if (writably_mapped) {
+				int j;
+
+				for (j = 0; j < thp_nr_pages(page); j++)
+					flush_dcache_page(page + j);
+			}
 
-			copied = copy_page_to_iter(pvec.pages[i], offset, bytes, iter);
+			copied = copy_page_to_iter(page, offset, bytes, iter);
 
 			written += copied;
 			iocb->ki_pos += copied;
@@ -2514,6 +2561,7 @@ ssize_t generic_file_buffered_read(struc
 put_pages:
 		for (i = 0; i < pagevec_count(&pvec); i++)
 			put_page(pvec.pages[i]);
+		pagevec_reinit(&pvec);
 	} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
 
 	file_accessed(filp);
_

Patches currently in -mm which might be from willy@infradead.org are

mm-debug-improve-memcg-debugging.patch
mm-filemap-rename-generic_file_buffered_read-subfunctions.patch
mm-filemap-remove-dynamically-allocated-array-from-filemap_read.patch
mm-filemap-convert-filemap_get_pages-to-take-a-pagevec.patch
mm-filemap-use-head-pages-in-generic_file_buffered_read.patch
mm-filemap-pass-a-sleep-state-to-put_and_wait_on_page_locked.patch
mm-filemap-support-readpage-splitting-a-page.patch
mm-filemap-inline-__wait_on_page_locked_async-into-caller.patch
mm-filemap-dont-call-readpage-if-iocb_waitq-is-set.patch
mm-filemap-change-filemap_read_page-calling-conventions.patch
mm-filemap-change-filemap_create_page-calling-conventions.patch
mm-filemap-convert-filemap_update_page-to-return-an-errno.patch
mm-filemap-move-the-iocb-checks-into-filemap_update_page.patch
mm-filemap-add-filemap_range_uptodate.patch
mm-filemap-split-filemap_readahead-out-of-filemap_get_pages.patch
mm-filemap-restructure-filemap_get_pages.patch
mm-filemap-dont-relock-the-page-after-calling-readpage.patch
mm-make-pagecache-tagged-lookups-return-only-head-pages.patch
mm-shmem-use-pagevec_lookup-in-shmem_unlock_mapping.patch
mm-swap-optimise-get_shadow_from_swap_cache.patch
mm-add-fgp_entry.patch
mm-filemap-rename-find_get_entry-to-mapping_get_entry.patch
mm-filemap-add-helper-for-finding-pages.patch
mm-filemap-add-helper-for-finding-pages-fix.patch
mm-filemap-add-mapping_seek_hole_data.patch
mm-filemap-add-mapping_seek_hole_data-fix.patch
iomap-use-mapping_seek_hole_data.patch
mm-add-and-use-find_lock_entries.patch
mm-add-and-use-find_lock_entries-fix.patch
mm-add-an-end-parameter-to-find_get_entries.patch
mm-add-an-end-parameter-to-pagevec_lookup_entries.patch
mm-remove-nr_entries-parameter-from-pagevec_lookup_entries.patch
mm-pass-pvec-directly-to-find_get_entries.patch
mm-remove-pagevec_lookup_entries.patch