[PATCHv3 29/41] ext4: make ext4_mpage_readpages() hugepage-aware

Kirill A. Shutemov
2016-09-15T11:55:11Z

This patch modifies ext4_mpage_readpages() to deal with huge pages.

We read out 2M at once, so we have to alloc (HPAGE_PMD_NR *
blocks_per_page) sector_t for that. I'm not entirely happy with kmalloc
in this codepath, but don't see any other option.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
fs/ext4/readpage.c | 38 ++++++++++++++++++++++++++++++++------
1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index a81b829d56de..6d7cbddceeb2 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -104,12 +104,12 @@ int ext4_mpage_readpages(struct address_space *mapping,

struct inode *inode = mapping->host;
const unsigned blkbits = inode->i_blkbits;
- const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
const unsigned blocksize = 1 << blkbits;
sector_t block_in_file;
sector_t last_block;
sector_t last_block_in_file;
- sector_t blocks[MAX_BUF_PER_PAGE];
+ sector_t blocks_on_stack[MAX_BUF_PER_PAGE];
+ sector_t *blocks = blocks_on_stack;
unsigned page_block;
struct block_device *bdev = inode->i_sb->s_bdev;
int length;
@@ -122,8 +122,9 @@ int ext4_mpage_readpages(struct address_space *mapping,
map.m_flags = 0;

for (; nr_pages; nr_pages--) {
- int fully_mapped = 1;
- unsigned first_hole = blocks_per_page;
+ int fully_mapped = 1, nr = nr_pages;
+ unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+ unsigned first_hole;

prefetchw(&page->flags);
if (pages) {
@@ -138,10 +139,31 @@ int ext4_mpage_readpages(struct address_space *mapping,
goto confused;

block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
- last_block = block_in_file + nr_pages * blocks_per_page;
+
+ if (PageTransHuge(page)) {
+ BUILD_BUG_ON(BIO_MAX_PAGES < HPAGE_PMD_NR);
+ nr = HPAGE_PMD_NR * blocks_per_page;
+ /* XXX: need a better solution ? */
+ blocks = kmalloc(sizeof(sector_t) * nr, GFP_NOFS);
+ if (!blocks) {
+ if (pages) {
+ delete_from_page_cache(page);
+ goto next_page;
+ }
+ return -ENOMEM;
+ }
+
+ blocks_per_page *= HPAGE_PMD_NR;
+ last_block = block_in_file + blocks_per_page;
+ } else {
+ blocks = blocks_on_stack;
+ last_block = block_in_file + nr * blocks_per_page;
+ }
+
last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
if (last_block > last_block_in_file)
last_block = last_block_in_file;
+ first_hole = blocks_per_page;
page_block = 0;

/*
@@ -213,6 +235,8 @@ int ext4_mpage_readpages(struct address_space *mapping,
}
}
if (first_hole != blocks_per_page) {
+ if (PageTransHuge(page))
+ goto confused;
zero_user_segment(page, first_hole << blkbits,
PAGE_SIZE);
if (first_hole == 0) {
@@ -248,7 +272,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
goto set_error_page;
}
bio = bio_alloc(GFP_KERNEL,
- min_t(int, nr_pages, BIO_MAX_PAGES));
+ min_t(int, nr, BIO_MAX_PAGES));
if (!bio) {
if (ctx)
fscrypt_release_ctx(ctx);
@@ -289,5 +313,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
BUG_ON(pages && !list_empty(pages));
if (bio)
submit_bio(bio);
+ if (blocks != blocks_on_stack)
+ kfree(blocks);
return 0;
}