From: Josef Bacik <josef@redhat.com>
To: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@vger.kernel.org
Subject: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
Date: Mon, 3 May 2010 13:27:02 -0400 [thread overview]
Message-ID: <20100503172702.GB3961@localhost.localdomain> (raw)
This is similar to what already happens in the write case. If we have a short
read while doing O_DIRECT, instead of just returning, fallthrough and try to
read the rest via buffered IO. BTRFS needs this because if we encounter a
compressed or inline extent during DIO, we need to fallback on buffered. If the
extent is compressed we need to read the entire thing into memory and
de-compress it into the users pages. I have tested this with fsx and everything
works great. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
---
mm/filemap.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 140ebda..423b439 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1263,7 +1263,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
{
struct file *filp = iocb->ki_filp;
ssize_t retval;
- unsigned long seg;
+ unsigned long seg = 0;
size_t count;
loff_t *ppos = &iocb->ki_pos;
@@ -1290,21 +1290,34 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
retval = mapping->a_ops->direct_IO(READ, iocb,
iov, pos, nr_segs);
}
- if (retval > 0)
+ if (retval > 0) {
*ppos = pos + retval;
- if (retval) {
+ count -= retval;
+ }
+ if (retval < 0 || !count) {
file_accessed(filp);
goto out;
}
}
}
+ count = retval;
for (seg = 0; seg < nr_segs; seg++) {
read_descriptor_t desc;
+ loff_t offset = 0;
+
+ if (count) {
+ if (count > iov[seg].iov_len) {
+ count -= iov[seg].iov_len;
+ continue;
+ }
+ offset = count;
+ count = 0;
+ }
desc.written = 0;
- desc.arg.buf = iov[seg].iov_base;
- desc.count = iov[seg].iov_len;
+ desc.arg.buf = iov[seg].iov_base + offset;
+ desc.count = iov[seg].iov_len - offset;
if (desc.count == 0)
continue;
desc.error = 0;
--
1.6.6.1
next reply other threads:[~2010-05-03 17:27 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-03 17:27 Josef Bacik [this message]
2010-05-04 0:14 ` [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO Dave Chinner
2010-05-04 15:27 ` Josef Bacik
2010-05-04 23:07 ` Dave Chinner
-- strict thread matches above, loose matches on Subject: below --
2010-05-03 16:11 Josef Bacik
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