[PATCHv6 17/37] fs: make block_read_full_page() be able to read huge page

Kirill A. Shutemov
2017-01-26T11:57:59Z

The approach is straight-forward: for compound pages we read out whole
huge page.

For huge page we cannot have array of buffer head pointers on stack --
it's 4096 pointers on x86-64 -- 'arr' is allocated with kmalloc() for
huge pages.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
fs/buffer.c | 22 +++++++++++++++++-----
include/linux/buffer_head.h | 9 +++++----
include/linux/page-flags.h | 2 +-
3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 0e87401cf335..72462beca909 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -871,7 +871,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,

try_again:
head = NULL;
- offset = PAGE_SIZE;
+ offset = hpage_size(page);
while ((offset -= size) >= 0) {
bh = alloc_buffer_head(GFP_NOFS);
if (!bh)
@@ -1466,7 +1466,7 @@ void set_bh_page(struct buffer_head *bh,
struct page *page, unsigned long offset)
{
bh->b_page = page;
- BUG_ON(offset >= PAGE_SIZE);
+ BUG_ON(offset >= hpage_size(page));
if (PageHighMem(page))
/*
* This catches illegal uses and preserves the offset:
@@ -2280,11 +2280,13 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
{
struct inode *inode = page->mapping->host;
sector_t iblock, lblock;
- struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+ struct buffer_head *arr_on_stack[MAX_BUF_PER_PAGE];
+ struct buffer_head *bh, *head, **arr = arr_on_stack;
unsigned int blocksize, bbits;
int nr, i;
int fully_mapped = 1;

+ VM_BUG_ON_PAGE(PageTail(page), page);
head = create_page_buffers(page, inode, 0);
blocksize = head->b_size;
bbits = block_size_bits(blocksize);
@@ -2295,6 +2297,11 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
nr = 0;
i = 0;

+ if (PageTransHuge(page)) {
+ arr = kmalloc(sizeof(struct buffer_head *) * HPAGE_PMD_NR *
+ MAX_BUF_PER_PAGE, GFP_NOFS);
+ }
+
do {
if (buffer_uptodate(bh))
continue;
@@ -2310,7 +2317,9 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
SetPageError(page);
}
if (!buffer_mapped(bh)) {
- zero_user(page, i * blocksize, blocksize);
+ zero_user(page + (i * blocksize / PAGE_SIZE),
+ i * blocksize % PAGE_SIZE,
+ blocksize);
if (!err)
set_buffer_uptodate(bh);
continue;
@@ -2336,7 +2345,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
if (!PageError(page))
SetPageUptodate(page);
unlock_page(page);
- return 0;
+ goto out;
}

/* Stage two: lock the buffers */
@@ -2358,6 +2367,9 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
else
submit_bh(REQ_OP_READ, 0, bh);
}
+out:
+ if (arr != arr_on_stack)
+ kfree(arr);
return 0;
}
EXPORT_SYMBOL(block_read_full_page);
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index fd4134ce9c54..f12f6293ed44 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -131,13 +131,14 @@ BUFFER_FNS(Meta, meta)
BUFFER_FNS(Prio, prio)
BUFFER_FNS(Defer_Completion, defer_completion)

-#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
+#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~hpage_mask(bh->b_page))

/* If we *know* page->private refers to buffer_heads */
-#define page_buffers(page) \
+#define page_buffers(__page) \
({ \
- BUG_ON(!PagePrivate(page)); \
- ((struct buffer_head *)page_private(page)); \
+ struct page *p = compound_head(__page); \
+ BUG_ON(!PagePrivate(p)); \
+ ((struct buffer_head *)page_private(p)); \
})
#define page_has_buffers(page) PagePrivate(page)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b85b73cfb1b3..23534bd47c08 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -746,7 +746,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
*/
static inline int page_has_private(struct page *page)
{
- return !!(page->flags & PAGE_FLAGS_PRIVATE);
+ return !!(compound_head(page)->flags & PAGE_FLAGS_PRIVATE);
}

#undef PF_ANY