Skip to content

Commit

Permalink
iomap: add support for sub-pagesize buffered I/O without buffer heads
Browse files Browse the repository at this point in the history 
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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  • Loading branch information
Christoph Hellwig authored and Darrick J. Wong committed Jul 12, 2018
1 parent ac8ee54 commit 9dc55f1
Show file tree
Hide file tree
Showing 2 changed files with 290 additions and 21 deletions.
280 changes: 259 additions & 21 deletions fs/iomap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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);
}

Expand All @@ -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) {
Expand All @@ -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;
}

Expand All @@ -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;
Expand All @@ -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
Expand All @@ -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,
Expand Down Expand Up @@ -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)
{
Expand All @@ -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;
}

Expand All @@ -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,
poff, plen, from, to, iomap);

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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down
Loading

0 comments on commit 9dc55f1

Please sign in to comment.