[PATCH 04/15] iomap: Support large pages

From: Matthew Wilcox
Date: Tue Sep 24 2019 - 20:53:25 EST

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From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

Change iomap_page from a statically sized uptodate bitmap to a dynamically
allocated uptodate bitmap, allowing an arbitrarily large page.

The only remaining places where iomap assumes an order-0 page are for
files with inline data, where there's no sense in allocating a larger
page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
fs/iomap/buffered-io.c | 119 ++++++++++++++++++++++++++---------------
include/linux/iomap.h | 2 +-
include/linux/mm.h | 2 +
3 files changed, 80 insertions(+), 43 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 0e76a4b6d98a..15d844a88439 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -23,14 +23,14 @@ static struct iomap_page *
iomap_page_create(struct inode *inode, struct page *page)
{
struct iomap_page *iop = to_iomap_page(page);
+ unsigned int n;

if (iop || i_blocks_per_page(inode, page) <= 1)
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);
+ n = BITS_TO_LONGS(i_blocks_per_page(inode, page));
+ iop = kmalloc(struct_size(iop, uptodate, n),
+ GFP_NOFS | __GFP_NOFAIL | __GFP_ZERO);

/*
* migrate_page_move_mapping() assumes that pages with private data have
@@ -61,15 +61,16 @@ iomap_page_release(struct page *page)
* 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,
+iomap_adjust_read_range(struct inode *inode, struct page *page,
loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)
{
+ struct iomap_page *iop = to_iomap_page(page);
loff_t orig_pos = *pos;
loff_t isize = i_size_read(inode);
unsigned block_bits = inode->i_blkbits;
unsigned block_size = (1 << block_bits);
- unsigned poff = offset_in_page(*pos);
- unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
+ unsigned poff = offset_in_this_page(page, *pos);
+ unsigned plen = min_t(loff_t, page_size(page) - poff, length);
unsigned first = poff >> block_bits;
unsigned last = (poff + plen - 1) >> block_bits;

@@ -107,7 +108,8 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
* page cache for blocks that are entirely outside of i_size.
*/
if (orig_pos <= isize && orig_pos + length > isize) {
- unsigned end = offset_in_page(isize - 1) >> block_bits;
+ unsigned end = offset_in_this_page(page, isize - 1) >>
+ block_bits;

if (first <= end && last > end)
plen -= (last - end) * block_size;
@@ -121,19 +123,16 @@ 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 < i_blocks_per_page(inode, page); i++) {
- if (i >= first && i <= last)
- set_bit(i, iop->uptodate);
- else if (!test_bit(i, iop->uptodate))
- uptodate = false;
- }
+ struct inode *inode = page->mapping->host;
+ unsigned first = off >> inode->i_blkbits;
+ unsigned count = len >> inode->i_blkbits;
+
+ bitmap_set(iop->uptodate, first, count);
+ if (!bitmap_full(iop->uptodate, i_blocks_per_page(inode, page)))
+ uptodate = false;
}

if (uptodate && !PageError(page))
@@ -194,6 +193,7 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
return;

BUG_ON(page->index);
+ BUG_ON(PageCompound(page));
BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));

addr = kmap_atomic(page);
@@ -203,6 +203,16 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
SetPageUptodate(page);
}

+/*
+ * Estimate the number of vectors we need based on the current page size;
+ * if we're wrong we'll end up doing an overly large allocation or needing
+ * to do a second allocation, neither of which is a big deal.
+ */
+static unsigned int iomap_nr_vecs(struct page *page, loff_t length)
+{
+ return (length + page_size(page) - 1) >> page_shift(page);
+}
+
static loff_t
iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
struct iomap *iomap)
@@ -222,7 +232,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
}

/* zero post-eof blocks as the page may be mapped */
- iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
+ iomap_adjust_read_range(inode, page, &pos, length, &poff, &plen);
if (plen == 0)
goto done;

@@ -258,7 +268,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,

if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
- int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ int nr_vecs = iomap_nr_vecs(page, length);

if (ctx->bio)
submit_bio(ctx->bio);
@@ -293,9 +303,9 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
unsigned poff;
loff_t ret;

- for (poff = 0; poff < PAGE_SIZE; poff += ret) {
- ret = iomap_apply(inode, page_offset(page) + poff,
- PAGE_SIZE - poff, 0, ops, &ctx,
+ for (poff = 0; poff < page_size(page); poff += ret) {
+ ret = iomap_apply(inode, file_offset_of_page(page) + poff,
+ page_size(page) - poff, 0, ops, &ctx,
iomap_readpage_actor);
if (ret <= 0) {
WARN_ON_ONCE(ret == 0);
@@ -328,7 +338,7 @@ iomap_next_page(struct inode *inode, struct list_head *pages, loff_t pos,
while (!list_empty(pages)) {
struct page *page = lru_to_page(pages);

- if (page_offset(page) >= (u64)pos + length)
+ if (file_offset_of_page(page) >= (u64)pos + length)
break;

list_del(&page->lru);
@@ -342,7 +352,7 @@ iomap_next_page(struct inode *inode, struct list_head *pages, loff_t pos,
* readpages call itself as every page gets checked again once
* actually needed.
*/
- *done += PAGE_SIZE;
+ *done += page_size(page);
put_page(page);
}

@@ -355,9 +365,14 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
{
struct iomap_readpage_ctx *ctx = data;
loff_t done, ret;
+ size_t left = 0;
+
+ if (ctx->cur_page)
+ left = page_size(ctx->cur_page) -
+ offset_in_this_page(ctx->cur_page, pos);

for (done = 0; done < length; done += ret) {
- if (ctx->cur_page && offset_in_page(pos + done) == 0) {
+ if (ctx->cur_page && left == 0) {
if (!ctx->cur_page_in_bio)
unlock_page(ctx->cur_page);
put_page(ctx->cur_page);
@@ -369,14 +384,27 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
if (!ctx->cur_page)
break;
ctx->cur_page_in_bio = false;
+ left = page_size(ctx->cur_page);
}
ret = iomap_readpage_actor(inode, pos + done, length - done,
ctx, iomap);
+ left -= ret;
}

return done;
}

+/* move to fs.h? */
+static inline struct page *readahead_first_page(struct list_head *head)
+{
+ return list_entry(head->prev, struct page, lru);
+}
+
+static inline struct page *readahead_last_page(struct list_head *head)
+{
+ return list_entry(head->next, struct page, lru);
+}
+
int
iomap_readpages(struct address_space *mapping, struct list_head *pages,
unsigned nr_pages, const struct iomap_ops *ops)
@@ -385,9 +413,10 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages,
.pages = pages,
.is_readahead = true,
};
- loff_t pos = page_offset(list_entry(pages->prev, struct page, lru));
- loff_t last = page_offset(list_entry(pages->next, struct page, lru));
- loff_t length = last - pos + PAGE_SIZE, ret = 0;
+ loff_t pos = file_offset_of_page(readahead_first_page(pages));
+ loff_t end = file_offset_of_next_page(readahead_last_page(pages));
+ loff_t length = end - pos;
+ loff_t ret = 0;

while (length > 0) {
ret = iomap_apply(mapping->host, pos, length, 0, ops,
@@ -410,7 +439,7 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages,
}

/*
- * Check that we didn't lose a page due to the arcance calling
+ * Check that we didn't lose a page due to the arcane calling
* conventions..
*/
WARN_ON_ONCE(!ret && !list_empty(ctx.pages));
@@ -435,7 +464,7 @@ iomap_is_partially_uptodate(struct page *page, unsigned long from,
unsigned i;

/* Limit range to one page */
- len = min_t(unsigned, PAGE_SIZE - from, count);
+ len = min_t(unsigned, page_size(page) - from, count);

/* First and last blocks in range within page */
first = from >> inode->i_blkbits;
@@ -474,7 +503,7 @@ 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) {
+ if (offset == 0 && len == page_size(page)) {
WARN_ON_ONCE(PageWriteback(page));
cancel_dirty_page(page);
iomap_page_release(page);
@@ -550,18 +579,20 @@ 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 from = offset_in_page(pos), to = from + len, poff, plen;
+ unsigned from = offset_in_this_page(page, pos);
+ unsigned to = from + len;
+ unsigned poff, plen;
int status = 0;

if (PageUptodate(page))
return 0;
+ iomap_page_create(inode, page);

do {
- iomap_adjust_read_range(inode, iop, &block_start,
+ iomap_adjust_read_range(inode, page, &block_start,
block_end - block_start, &poff, &plen);
if (plen == 0)
break;
@@ -673,7 +704,7 @@ __iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
*/
if (unlikely(copied < len && !PageUptodate(page)))
return 0;
- iomap_set_range_uptodate(page, offset_in_page(pos), len);
+ iomap_set_range_uptodate(page, offset_in_this_page(page, pos), len);
iomap_set_page_dirty(page);
return copied;
}
@@ -685,6 +716,7 @@ iomap_write_end_inline(struct inode *inode, struct page *page,
void *addr;

WARN_ON_ONCE(!PageUptodate(page));
+ BUG_ON(PageCompound(page));
BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));

addr = kmap_atomic(page);
@@ -749,6 +781,10 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
unsigned long bytes; /* Bytes to write to page */
size_t copied; /* Bytes copied from user */

+ /*
+ * XXX: We don't know what size page we'll find in the
+ * page cache, so only copy up to a regular page boundary.
+ */
offset = offset_in_page(pos);
bytes = min_t(unsigned long, PAGE_SIZE - offset,
iov_iter_count(i));
@@ -1041,19 +1077,18 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
lock_page(page);
size = i_size_read(inode);
if ((page->mapping != inode->i_mapping) ||
- (page_offset(page) > size)) {
+ (file_offset_of_page(page) > size)) {
/* We overload EFAULT to mean page got truncated */
ret = -EFAULT;
goto out_unlock;
}

- /* page is wholly or partially inside EOF */
- if (((page->index + 1) << PAGE_SHIFT) > size)
- length = offset_in_page(size);
+ offset = file_offset_of_page(page);
+ if (size - offset < page_size(page))
+ length = offset_in_this_page(page, size);
else
- length = PAGE_SIZE;
+ length = page_size(page);

- offset = page_offset(page);
while (length > 0) {
ret = iomap_apply(inode, offset, length,
IOMAP_WRITE | IOMAP_FAULT, ops, page,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index bc499ceae392..86be24a8259b 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -139,7 +139,7 @@ loff_t iomap_apply(struct inode *inode, loff_t pos, loff_t length,
struct iomap_page {
atomic_t read_count;
atomic_t write_count;
- DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
+ unsigned long uptodate[];
};

static inline struct iomap_page *to_iomap_page(struct page *page)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 294a67b94147..04bea9f9282c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1415,6 +1415,8 @@ static inline void clear_page_pfmemalloc(struct page *page)
extern void pagefault_out_of_memory(void);

#define offset_in_page(p) ((unsigned long)(p) & ~PAGE_MASK)
+#define offset_in_this_page(page, p) \
+ ((unsigned long)(p) & (page_size(page) - 1))

/*
* Flags passed to show_mem() and show_free_areas() to suppress output in
--
2.23.0

Next message: Matthew Wilcox: "[RFC 00/15] Large pages in the page-cache"
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Next in thread: Matthew Wilcox: "[PATCH 10/15] mm: Allow find_get_page to be used for large pages"
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