* [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
@ 2010-05-03 17:27 Josef Bacik
2010-05-04 0:14 ` Dave Chinner
0 siblings, 1 reply; 5+ messages in thread
From: Josef Bacik @ 2010-05-03 17:27 UTC (permalink / raw)
To: linux-btrfs, linux-fsdevel, linux-kernel, linux-mm
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
2010-05-03 17:27 [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO Josef Bacik
@ 2010-05-04 0:14 ` Dave Chinner
2010-05-04 15:27 ` Josef Bacik
0 siblings, 1 reply; 5+ messages in thread
From: Dave Chinner @ 2010-05-04 0:14 UTC (permalink / raw)
To: Josef Bacik; +Cc: linux-btrfs, linux-fsdevel, linux-kernel, linux-mm
On Mon, May 03, 2010 at 01:27:02PM -0400, Josef Bacik wrote:
> 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,
Won't this mean that any direct IO read that spans EOF (i.e. get a
short read) now attempt a buffered IO (that will fail) before returning?
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
2010-05-04 0:14 ` Dave Chinner
@ 2010-05-04 15:27 ` Josef Bacik
2010-05-04 23:07 ` Dave Chinner
0 siblings, 1 reply; 5+ messages in thread
From: Josef Bacik @ 2010-05-04 15:27 UTC (permalink / raw)
To: Dave Chinner
Cc: Josef Bacik, linux-btrfs, linux-fsdevel, linux-kernel, linux-mm
On Tue, May 04, 2010 at 10:14:18AM +1000, Dave Chinner wrote:
> On Mon, May 03, 2010 at 01:27:02PM -0400, Josef Bacik wrote:
> > 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,
>
> Won't this mean that any direct IO read that spans EOF (i.e. get a
> short read) now attempt a buffered IO (that will fail) before returning?
>
Hmm yeah you are right. What would be an acceptable way to avoid this, do a
if (retval || !count || ppos >= i_size_read(inode))
goto out;
type thing? Thanks,
Josef
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
2010-05-04 15:27 ` Josef Bacik
@ 2010-05-04 23:07 ` Dave Chinner
0 siblings, 0 replies; 5+ messages in thread
From: Dave Chinner @ 2010-05-04 23:07 UTC (permalink / raw)
To: Josef Bacik; +Cc: linux-btrfs, linux-fsdevel, linux-kernel, linux-mm
On Tue, May 04, 2010 at 11:27:50AM -0400, Josef Bacik wrote:
> On Tue, May 04, 2010 at 10:14:18AM +1000, Dave Chinner wrote:
> > On Mon, May 03, 2010 at 01:27:02PM -0400, Josef Bacik wrote:
> > > 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,
> >
> > Won't this mean that any direct IO read that spans EOF (i.e. get a
> > short read) now attempt a buffered IO (that will fail) before returning?
> >
>
> Hmm yeah you are right. What would be an acceptable way to avoid this, do a
>
> if (retval || !count || ppos >= i_size_read(inode))
> goto out;
>
> type thing? Thanks,
Yes, that looks like it would work to me. Might be worth a comment,
though.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
@ 2010-05-03 16:11 Josef Bacik
0 siblings, 0 replies; 5+ messages in thread
From: Josef Bacik @ 2010-05-03 16:11 UTC (permalink / raw)
To: linux-btrfs, linux-fsdevel, linux-kernel, linux-mm; +Cc: Josef Bacik
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 | 19 +++++++++++++++----
1 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 140ebda..cc804d9 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;
@@ -1292,19 +1292,30 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
}
if (retval > 0)
*ppos = pos + retval;
- if (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
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2010-05-03 17:27 [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO Josef Bacik
2010-05-04 0:14 ` Dave Chinner
2010-05-04 15:27 ` Josef Bacik
2010-05-04 23:07 ` Dave Chinner
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