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Subject[RFC DRAFT PATCH] per-buffered-write stream IDs
Date
Hi Jens,

This RFC DRAFT patch is on top of your "[PATCH v2] Support for write stream IDs"
I throw it out early to get comments if it's the way to go.

Quote LWN(http://lwn.net/Articles/638722):

"There would be clear value in a closer association between stream IDs
and specific buffered-write operations. Getting there would require storing
the stream ID with each dirtied page, though; that, in turn, almost certainly
implies shoehorning the stream ID into the associated page structure.
That would not be an easy task; it is not surprising that it is not a part of
this patch set. Should the lack of per-buffered-write stream IDs prove to be
a serious constraint in the future, somebody will certainly be motivated to
try to find a place to store another eight bits in struct page."

This draft patch stores stream_id in buffer head instead of page.

---
fs/buffer.c | 4 ++--
fs/ext4/page-io.c | 2 +-
fs/mpage.c | 5 ++++-
include/linux/buffer_head.h | 1 +
mm/filemap.c | 17 +++++++++++++++++
5 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 5191523..274fcc5 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1774,7 +1774,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
do {
struct buffer_head *next = bh->b_this_page;
if (buffer_async_write(bh)) {
- _submit_bh(write_op, bh, streamid_to_flags(inode_streamid(inode)));
+ _submit_bh(write_op, bh, streamid_to_flags(bh->b_streamid));
nr_underway++;
}
bh = next;
@@ -1828,7 +1828,7 @@ recover:
struct buffer_head *next = bh->b_this_page;
if (buffer_async_write(bh)) {
clear_buffer_dirty(bh);
- _submit_bh(write_op, bh, streamid_to_flags(inode_streamid(inode)));
+ _submit_bh(write_op, bh, streamid_to_flags(bh->b_streamid));
nr_underway++;
}
bh = next;
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 980c5a9..c912129 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -406,7 +406,7 @@ submit_and_retry:
ret = io_submit_init_bio(io, bh);
if (ret)
return ret;
- bio_set_streamid(io->io_bio, inode_streamid(inode));
+ bio_set_streamid(io->io_bio, bh->b_streamid);
}
ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
if (ret != bh->b_size)
diff --git a/fs/mpage.c b/fs/mpage.c
index fba13f4..1c5ae1c 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -481,12 +481,15 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
int length;
struct buffer_head map_bh;
loff_t i_size = i_size_read(inode);
+ int streamid = 0;
int ret = 0;

if (page_has_buffers(page)) {
struct buffer_head *head = page_buffers(page);
struct buffer_head *bh = head;

+ streamid = bh->b_streamid;
+
/* If they're all mapped and dirty, do it */
page_block = 0;
do {
@@ -605,7 +608,7 @@ alloc_new:
bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
if (bio == NULL)
goto confused;
- bio_set_streamid(bio, inode_streamid(inode));
+ bio_set_streamid(bio, streamid);
}

/*
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 73b4522..5dbb460 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -75,6 +75,7 @@ struct buffer_head {
struct address_space *b_assoc_map; /* mapping this buffer is
associated with */
atomic_t b_count; /* users using this buffer_head */
+ unsigned int b_streamid;
};

/*
diff --git a/mm/filemap.c b/mm/filemap.c
index 6bf5e42..3a31b95 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2419,6 +2419,21 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
}
EXPORT_SYMBOL(grab_cache_page_write_begin);

+static void buffer_head_set_streamid(struct page *page, struct file *file)
+{
+ struct buffer_head *bh, *head;
+
+ if (!page_has_buffers(page))
+ return;
+
+ head = page_buffers(page);
+ bh = head;
+ do {
+ bh->b_streamid = file->f_streamid;
+ bh = bh->b_this_page;
+ } while (bh != head);
+}
+
ssize_t generic_perform_write(struct file *file,
struct iov_iter *i, loff_t pos)
{
@@ -2466,6 +2481,8 @@ again:
if (unlikely(status < 0))
break;

+ buffer_head_set_streamid(page, file);
+
if (mapping_writably_mapped(mapping))
flush_dcache_page(page);

--
1.9.1


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