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Subject[RFC PATCH v3 3/7] swap: use direct I/O for SWP_FILE swap_readpage
Date
On Mon, Nov 17, 2014 at 07:48:17AM -0800, Christoph Hellwig wrote:
> With the new iov_iter infrastructure that supprots direct I/O to kernel
> pages please get rid of the ->readpage hack first. I'm still utterly
> disapoined that this crap ever got merged.

Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
---
mm/page_io.c | 32 ++++++++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 955db8b..10715e0 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -283,8 +283,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,

set_page_writeback(page);
unlock_page(page);
- ret = mapping->a_ops->direct_IO(ITER_BVEC | WRITE,
- &kiocb, &from,
+ ret = mapping->a_ops->direct_IO(WRITE, &kiocb, &from,
kiocb.ki_pos);
if (ret == PAGE_SIZE) {
count_vm_event(PSWPOUT);
@@ -348,12 +347,37 @@ int swap_readpage(struct page *page)
}

if (sis->flags & SWP_FILE) {
+ struct kiocb kiocb;
struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;
+ struct bio_vec bv = {
+ .bv_page = page,
+ .bv_len = PAGE_SIZE,
+ .bv_offset = 0,
+ };
+ struct iov_iter to = {
+ .type = ITER_BVEC | READ,
+ .count = PAGE_SIZE,
+ .iov_offset = 0,
+ .nr_segs = 1,
+ };
+ to.bvec = &bv; /* older gcc versions are broken */
+
+ init_sync_kiocb(&kiocb, swap_file);
+ kiocb.ki_pos = page_file_offset(page);
+ kiocb.ki_nbytes = PAGE_SIZE;

- ret = mapping->a_ops->readpage(swap_file, page);
- if (!ret)
+ ret = mapping->a_ops->direct_IO(READ, &kiocb, &to,
+ kiocb.ki_pos);
+ if (ret == PAGE_SIZE) {
+ SetPageUptodate(page);
count_vm_event(PSWPIN);
+ ret = 0;
+ } else {
+ ClearPageUptodate(page);
+ SetPageError(page);
+ }
+ unlock_page(page);
return ret;
}

--
2.1.3


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