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@xxxxxx>
---
fs/iomap.c | 247 +++++++++++++++++++++++++++++++++++++++---
include/linux/iomap.h | 31 ++++++
2 files changed, 260 insertions(+), 18 deletions(-)
diff --git a/fs/iomap.c b/fs/iomap.c
index debb859a8a14..ea746e0287f9 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -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 +105,107 @@ 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;
+}
+
+/*
+ * 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 poff = *pos & (PAGE_SIZE - 1);
+ unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
+
+ if (iop) {
+ unsigned block_size = i_blocksize(inode);
+ unsigned first = poff >> inode->i_blkbits;
+ unsigned last = (poff + plen - 1) >> inode->i_blkbits;
+ 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;
+ }
+
+ /* 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;
+ break;
+ }
+ }
+ }
+
+ *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_end_io(struct bio *bio)
{
@@ -112,7 +214,7 @@ 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);
}
@@ -142,18 +244,19 @@ 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;
- /* we don't support blocksize < PAGE_SIZE quite yet: */
- WARN_ON_ONCE(pos != page_offset(page));
- WARN_ON_ONCE(plen != PAGE_SIZE);
+ 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;
}
@@ -169,6 +272,14 @@ 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)) {
if (ctx->bio)
submit_bio(ctx->bio);
@@ -177,7 +288,7 @@ 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;
+ return pos - orig_pos + plen;
}
int
@@ -188,8 +299,6 @@ 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,
@@ -295,6 +404,92 @@ 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)
+{
+ struct iomap_page *iop = to_iomap_page(page);
+
+ /*
+ * 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;
+
+ if (iop) {
+ 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);
+ }
+ 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) {
+ cancel_dirty_page(page);
+ iomap_releasepage(page, GFP_NOIO);
+ }
+}
+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)
{
@@ -318,6 +513,7 @@ 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;
}
@@ -333,6 +529,7 @@ 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);
@@ -340,15 +537,29 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,
unsigned plen = min_t(loff_t, PAGE_SIZE - poff, block_end - block_start);
unsigned from = pos & (PAGE_SIZE - 1);
unsigned to = from + len;
-
- WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);
+ int status;
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)
+ return status;
+ }
+
+ block_start += plen;
+ } while (poff + plen < PAGE_SIZE);
+
+ return 0;
}
static int
@@ -429,7 +640,7 @@ __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);
@@ -741,7 +952,7 @@ 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;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 4d3d9d0cd69f..7f8787a1bbce 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -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;
@@ -88,12 +91,40 @@ 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,
--
2.17.0
