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Commit 9dc55f13 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Darrick J. Wong
Browse files

iomap: add support for sub-pagesize buffered I/O without buffer heads 



After already supporting a simple implementation of buffered writes for
the blocksize == PAGE_SIZE case in the last commit this adds full support
even for smaller block sizes.   There are three bits of per-block
information in the buffer_head structure that really matter for the iomap
read and write path:

 - uptodate status (BH_uptodate)
 - marked as currently under read I/O (BH_Async_Read)
 - marked as currently under write I/O (BH_Async_Write)

Instead of having new per-block structures this now adds a per-page
structure called struct iomap_page to track this information in a slightly
different form:

 - a bitmap for the per-block uptodate status.  For worst case of a 64k
   page size system this bitmap needs to contain 128 bits.  For the
   typical 4k page size case it only needs 8 bits, although we still
   need a full unsigned long due to the way the atomic bitmap API works.
 - two atomic_t counters are used to track the outstanding read and write
   counts

There is quite a bit of boilerplate code as the buffered I/O path uses
various helper methods, but the actual code is very straight forward.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent ac8ee546

fs/iomap.c

+259 −21
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <linux/iomap.h>

#include <linux/uaccess.h>

#include <linux/gfp.h>

#include <linux/migrate.h>

#include <linux/mm.h>

#include <linux/mm_inline.h>

#include <linux/swap.h>
@@ -104,6 +105,138 @@ iomap_sector(struct iomap *iomap, loff_t pos) 
	return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;

}



static struct iomap_page *

iomap_page_create(struct inode *inode, struct page *page)

{

	struct iomap_page *iop = to_iomap_page(page);



	if (iop || i_blocksize(inode) == PAGE_SIZE)

		return iop;



	iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);

	atomic_set(&iop->read_count, 0);

	atomic_set(&iop->write_count, 0);

	bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);

	set_page_private(page, (unsigned long)iop);

	SetPagePrivate(page);

	return iop;

}



static void

iomap_page_release(struct page *page)

{

	struct iomap_page *iop = to_iomap_page(page);



	if (!iop)

		return;

	WARN_ON_ONCE(atomic_read(&iop->read_count));

	WARN_ON_ONCE(atomic_read(&iop->write_count));

	ClearPagePrivate(page);

	set_page_private(page, 0);

	kfree(iop);

}



/*

 * Calculate the range inside the page that we actually need to read.

 */

static void

iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,

		loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)

{

	unsigned block_bits = inode->i_blkbits;

	unsigned block_size = (1 << block_bits);

	unsigned poff = *pos & (PAGE_SIZE - 1);

	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);

	unsigned first = poff >> block_bits;

	unsigned last = (poff + plen - 1) >> block_bits;

	unsigned end = (i_size_read(inode) & (PAGE_SIZE - 1)) >> block_bits;



	/*

	 * If the block size is smaller than the page size we need to check the

	 * per-block uptodate status and adjust the offset and length if needed

	 * to avoid reading in already uptodate ranges.

	 */

	if (iop) {

		unsigned int i;



		/* move forward for each leading block marked uptodate */

		for (i = first; i <= last; i++) {

			if (!test_bit(i, iop->uptodate))

				break;

			*pos += block_size;

			poff += block_size;

			plen -= block_size;

			first++;

		}



		/* truncate len if we find any trailing uptodate block(s) */

		for ( ; i <= last; i++) {

			if (test_bit(i, iop->uptodate)) {

				plen -= (last - i + 1) * block_size;

				last = i - 1;

				break;

			}

		}

	}



	/*

	 * If the extent spans the block that contains the i_size we need to

	 * handle both halves separately so that we properly zero data in the

	 * page cache for blocks that are entirely outside of i_size.

	 */

	if (first <= end && last > end)

		plen -= (last - end) * block_size;



	*offp = poff;

	*lenp = plen;

}



static void

iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)

{

	struct iomap_page *iop = to_iomap_page(page);

	struct inode *inode = page->mapping->host;

	unsigned first = off >> inode->i_blkbits;

	unsigned last = (off + len - 1) >> inode->i_blkbits;

	unsigned int i;

	bool uptodate = true;



	if (iop) {

		for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {

			if (i >= first && i <= last)

				set_bit(i, iop->uptodate);

			else if (!test_bit(i, iop->uptodate))

				uptodate = false;

		}

	}



	if (uptodate && !PageError(page))

		SetPageUptodate(page);

}



static void

iomap_read_finish(struct iomap_page *iop, struct page *page)

{

	if (!iop || atomic_dec_and_test(&iop->read_count))

		unlock_page(page);

}



static void

iomap_read_page_end_io(struct bio_vec *bvec, int error)

{

	struct page *page = bvec->bv_page;

	struct iomap_page *iop = to_iomap_page(page);



	if (unlikely(error)) {

		ClearPageUptodate(page);

		SetPageError(page);

	} else {

		iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);

	}



	iomap_read_finish(iop, page);

}



static void

iomap_read_inline_data(struct inode *inode, struct page *page,

		struct iomap *iomap)
@@ -132,7 +265,7 @@ iomap_read_end_io(struct bio *bio) 
	int i;



	bio_for_each_segment_all(bvec, bio, i)

		page_endio(bvec->bv_page, false, error);

		iomap_read_page_end_io(bvec, error);

	bio_put(bio);

}
@@ -150,9 +283,10 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 
{

	struct iomap_readpage_ctx *ctx = data;

	struct page *page = ctx->cur_page;

	unsigned poff = pos & (PAGE_SIZE - 1);

	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);

	struct iomap_page *iop = iomap_page_create(inode, page);

	bool is_contig = false;

	loff_t orig_pos = pos;

	unsigned poff, plen;

	sector_t sector;



	if (iomap->type == IOMAP_INLINE) {
@@ -161,13 +295,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 
		return PAGE_SIZE;

	}



	/* we don't support blocksize < PAGE_SIZE quite yet. */

	WARN_ON_ONCE(pos != page_offset(page));

	WARN_ON_ONCE(plen != PAGE_SIZE);

	/* zero post-eof blocks as the page may be mapped */

	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);

	if (plen == 0)

		goto done;



	if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) {

		zero_user(page, poff, plen);

		SetPageUptodate(page);

		iomap_set_range_uptodate(page, poff, plen);

		goto done;

	}
@@ -183,6 +318,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 
		is_contig = true;

	}



	/*

	 * If we start a new segment we need to increase the read count, and we

	 * need to do so before submitting any previous full bio to make sure

	 * that we don't prematurely unlock the page.

	 */

	if (iop)

		atomic_inc(&iop->read_count);



	if (!ctx->bio || !is_contig || bio_full(ctx->bio)) {

		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);

		int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -203,7 +346,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 


	__bio_add_page(ctx->bio, page, plen, poff);

done:

	return plen;

	/*

	 * Move the caller beyond our range so that it keeps making progress.

	 * For that we have to include any leading non-uptodate ranges, but

	 * we can skip trailing ones as they will be handled in the next

	 * iteration.

	 */

	return pos - orig_pos + plen;

}



int
@@ -214,8 +363,6 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops) 
	unsigned poff;

	loff_t ret;



	WARN_ON_ONCE(page_has_buffers(page));



	for (poff = 0; poff < PAGE_SIZE; poff += ret) {

		ret = iomap_apply(inode, page_offset(page) + poff,

				PAGE_SIZE - poff, 0, ops, &ctx,
@@ -341,6 +488,84 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, 
}

EXPORT_SYMBOL_GPL(iomap_readpages);



int

iomap_is_partially_uptodate(struct page *page, unsigned long from,

		unsigned long count)

{

	struct iomap_page *iop = to_iomap_page(page);

	struct inode *inode = page->mapping->host;

	unsigned first = from >> inode->i_blkbits;

	unsigned last = (from + count - 1) >> inode->i_blkbits;

	unsigned i;



	if (iop) {

		for (i = first; i <= last; i++)

			if (!test_bit(i, iop->uptodate))

				return 0;

		return 1;

	}



	return 0;

}

EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);



int

iomap_releasepage(struct page *page, gfp_t gfp_mask)

{

	/*

	 * mm accommodates an old ext3 case where clean pages might not have had

	 * the dirty bit cleared. Thus, it can send actual dirty pages to

	 * ->releasepage() via shrink_active_list(), skip those here.

	 */

	if (PageDirty(page) || PageWriteback(page))

		return 0;

	iomap_page_release(page);

	return 1;

}

EXPORT_SYMBOL_GPL(iomap_releasepage);



void

iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)

{

	/*

	 * If we are invalidating the entire page, clear the dirty state from it

	 * and release it to avoid unnecessary buildup of the LRU.

	 */

	if (offset == 0 && len == PAGE_SIZE) {

		WARN_ON_ONCE(PageWriteback(page));

		cancel_dirty_page(page);

		iomap_page_release(page);

	}

}

EXPORT_SYMBOL_GPL(iomap_invalidatepage);



#ifdef CONFIG_MIGRATION

int

iomap_migrate_page(struct address_space *mapping, struct page *newpage,

		struct page *page, enum migrate_mode mode)

{

	int ret;



	ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);

	if (ret != MIGRATEPAGE_SUCCESS)

		return ret;



	if (page_has_private(page)) {

		ClearPagePrivate(page);

		set_page_private(newpage, page_private(page));

		set_page_private(page, 0);

		SetPagePrivate(newpage);

	}



	if (mode != MIGRATE_SYNC_NO_COPY)

		migrate_page_copy(newpage, page);

	else

		migrate_page_states(newpage, page);

	return MIGRATEPAGE_SUCCESS;

}

EXPORT_SYMBOL_GPL(iomap_migrate_page);

#endif /* CONFIG_MIGRATION */



static void

iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)

{
@@ -364,6 +589,7 @@ iomap_read_page_sync(struct inode *inode, loff_t block_start, struct page *page, 


	if (iomap->type != IOMAP_MAPPED || block_start >= i_size_read(inode)) {

		zero_user_segments(page, poff, from, to, poff + plen);

		iomap_set_range_uptodate(page, poff, plen);

		return 0;

	}
@@ -379,21 +605,33 @@ static int 
__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,

		struct page *page, struct iomap *iomap)

{

	struct iomap_page *iop = iomap_page_create(inode, page);

	loff_t block_size = i_blocksize(inode);

	loff_t block_start = pos & ~(block_size - 1);

	loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1);

	unsigned poff = block_start & (PAGE_SIZE - 1);

	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, block_end - block_start);

	unsigned from = pos & (PAGE_SIZE - 1), to = from + len;



	WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);

	unsigned from = pos & (PAGE_SIZE - 1), to = from + len, poff, plen;

	int status = 0;



	if (PageUptodate(page))

		return 0;

	if (from <= poff && to >= poff + plen)

		return 0;

	return iomap_read_page_sync(inode, block_start, page,



	do {

		iomap_adjust_read_range(inode, iop, &block_start,

				block_end - block_start, &poff, &plen);

		if (plen == 0)

			break;



		if ((from > poff && from < poff + plen) ||

		    (to > poff && to < poff + plen)) {

			status = iomap_read_page_sync(inode, block_start, page,

					poff, plen, from, to, iomap);

			if (status)

				break;

		}



	} while ((block_start += plen) < block_end);



	return status;

}



static int
@@ -476,7 +714,7 @@ __iomap_write_end(struct inode *inode, loff_t pos, unsigned len, 
	if (unlikely(copied < len && !PageUptodate(page))) {

		copied = 0;

	} else {

		SetPageUptodate(page);

		iomap_set_range_uptodate(page, pos & (PAGE_SIZE - 1), len);

		iomap_set_page_dirty(page);

	}

	return __generic_write_end(inode, pos, copied, page);
@@ -812,7 +1050,7 @@ iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length, 
		block_commit_write(page, 0, length);

	} else {

		WARN_ON_ONCE(!PageUptodate(page));

		WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);

		iomap_page_create(inode, page);

	}



	return length;

include/linux/iomap.h

+31 −0
Original line number Diff line number Diff line
@@ -2,6 +2,9 @@ 
#ifndef LINUX_IOMAP_H

#define LINUX_IOMAP_H 1



#include <linux/atomic.h>

#include <linux/bitmap.h>

#include <linux/mm.h>

#include <linux/types.h>



struct address_space;
@@ -98,12 +101,40 @@ struct iomap_ops { 
			ssize_t written, unsigned flags, struct iomap *iomap);

};



/*

 * Structure allocate for each page when block size < PAGE_SIZE to track

 * sub-page uptodate status and I/O completions.

 */

struct iomap_page {

	atomic_t		read_count;

	atomic_t		write_count;

	DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);

};



static inline struct iomap_page *to_iomap_page(struct page *page)

{

	if (page_has_private(page))

		return (struct iomap_page *)page_private(page);

	return NULL;

}



ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,

		const struct iomap_ops *ops);

int iomap_readpage(struct page *page, const struct iomap_ops *ops);

int iomap_readpages(struct address_space *mapping, struct list_head *pages,

		unsigned nr_pages, const struct iomap_ops *ops);

int iomap_set_page_dirty(struct page *page);

int iomap_is_partially_uptodate(struct page *page, unsigned long from,

		unsigned long count);

int iomap_releasepage(struct page *page, gfp_t gfp_mask);

void iomap_invalidatepage(struct page *page, unsigned int offset,

		unsigned int len);

#ifdef CONFIG_MIGRATION

int iomap_migrate_page(struct address_space *mapping, struct page *newpage,

		struct page *page, enum migrate_mode mode);

#else

#define iomap_migrate_page NULL

#endif

int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,

		const struct iomap_ops *ops);

int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,