Commit 6ad7c607 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

fs: reduce stack usage in __mpage_writepage 

Some architectures support a very large PAGE_SIZE, so instead of the 8
pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or
so many on Hexagon that it trips compiler warnings about exceeding stack
frame size.

All we're doing with this array is checking for block contiguity, which we
can as well do by remembering the address of the first block in the page
and checking this block is at the appropriate offset from that address.

Link: https://lkml.kernel.org/r/20231215200245.748418-4-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent e8ff8248

fs/mpage.c

+12 −8
Original line number Diff line number Diff line
@@ -466,7 +466,7 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;

	sector_t last_block;

	sector_t block_in_file;

	sector_t blocks[MAX_BUF_PER_PAGE];

	sector_t first_block;

	unsigned page_block;

	unsigned first_unmapped = blocks_per_page;

	struct block_device *bdev = NULL;
@@ -504,10 +504,12 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
			if (!buffer_dirty(bh) || !buffer_uptodate(bh))

				goto confused;

			if (page_block) {

				if (bh->b_blocknr != blocks[page_block-1] + 1)

				if (bh->b_blocknr != first_block + page_block)

					goto confused;

			} else {

				first_block = bh->b_blocknr;

			}

			blocks[page_block++] = bh->b_blocknr;

			page_block++;

			boundary = buffer_boundary(bh);

			if (boundary) {

				boundary_block = bh->b_blocknr;
@@ -556,10 +558,12 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
			boundary_bdev = map_bh.b_bdev;

		}

		if (page_block) {

			if (map_bh.b_blocknr != blocks[page_block-1] + 1)

			if (map_bh.b_blocknr != first_block + page_block)

				goto confused;

		} else {

			first_block = map_bh.b_blocknr;

		}

		blocks[page_block++] = map_bh.b_blocknr;

		page_block++;

		boundary = buffer_boundary(&map_bh);

		bdev = map_bh.b_bdev;

		if (block_in_file == last_block)
@@ -591,7 +595,7 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
	/*

	 * This page will go to BIO.  Do we need to send this BIO off first?

	 */

	if (bio && mpd->last_block_in_bio != blocks[0] - 1)

	if (bio && mpd->last_block_in_bio != first_block - 1)

		bio = mpage_bio_submit_write(bio);



alloc_new:
@@ -599,7 +603,7 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
		bio = bio_alloc(bdev, BIO_MAX_VECS,

				REQ_OP_WRITE | wbc_to_write_flags(wbc),

				GFP_NOFS);

		bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);

		bio->bi_iter.bi_sector = first_block << (blkbits - 9);

		wbc_init_bio(wbc, bio);

	}
@@ -627,7 +631,7 @@ static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, 
					boundary_block, 1 << blkbits);

		}

	} else {

		mpd->last_block_in_bio = blocks[blocks_per_page - 1];

		mpd->last_block_in_bio = first_block + blocks_per_page - 1;

	}

	goto out;