Commit cbd59c48 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
Browse files

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: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarKent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ff993ba1

mm/filemap.c

+85 −37
Original line number Diff line number Diff line
@@ -2178,6 +2178,51 @@ static int lock_page_for_iocb(struct kiocb *iocb, struct page *page) 
		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)

{
@@ -2331,15 +2376,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, 
	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;
@@ -2348,29 +2393,30 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, 


	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]))

	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);
@@ -2378,26 +2424,23 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, 


		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)
@@ -2442,6 +2485,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, 
		return 0;



	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);

	pagevec_init(&pvec);



	do {

		cond_resched();
@@ -2469,13 +2513,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, 
		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:
@@ -2489,24 +2528,32 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, 
		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;
@@ -2520,6 +2567,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, 
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);