Re: [PATCH -mm] readahead: partial sendfile fix
Ram Pai, Sorry for the long delay, I was just back from the winter vacation. On Mon, Feb 12, 2007 at 11:49:10AM -0800, Ram Pai wrote: > The solution you proposed seems kludgy to me. If you determine that the I dislike it, either. > its a restarted aio, then start reading from where readahead had left > reading from earlier. To me a simple fix is: > > - if (unlikely(aio_restarted())) > - next_index = last_index; /* Avoid repeat readahead */ > > + if (unlikely(aio_restarted())) > + next_index = min(prev_index+1, last_index); > > > No? Can be even simpler, if we _only_ want to fix the aio case: + if (unlikely(aio_restarted())) + next_index = prev_index + 1; Regards, Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH -mm] readahead: partial sendfile fix
Ram Pai, Sorry for the long delay, I was just back from the winter vacation. On Mon, Feb 12, 2007 at 11:49:10AM -0800, Ram Pai wrote: The solution you proposed seems kludgy to me. If you determine that the I dislike it, either. its a restarted aio, then start reading from where readahead had left reading from earlier. To me a simple fix is: - if (unlikely(aio_restarted())) - next_index = last_index; /* Avoid repeat readahead */ + if (unlikely(aio_restarted())) + next_index = min(prev_index+1, last_index); No? Can be even simpler, if we _only_ want to fix the aio case: + if (unlikely(aio_restarted())) + next_index = prev_index + 1; Regards, Wu - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH -mm] readahead: partial sendfile fix
On Sat, 2007-02-10 at 09:40 +0800, Fengguang Wu wrote:
> Enable readahead to handle partially done read requests, e.g.
>
> sendfile(188, 1921, [1478592], 19553028) = 37440
> sendfile(188, 1921, [1516032], 19515588) = 28800
> sendfile(188, 1921, [1544832], 19486788) = 37440
> sendfile(188, 1921, [1582272], 19449348) = 14400
> sendfile(188, 1921, [1596672], 19434948) = 37440
> sendfile(188, 1921, [1634112], 19397508) = 37440
>
> In the above strace log,
> - some lighttpd is doing _sequential_ reading
> - every sendfile() returns with only _partial_ work done
>
> page_cache_readahead() expects that if it returns @next_index, it will
> be
> called exactly at @next_index next time. That's not true here. So the
> pattern
> will be falsely recognized as a random read trace.
>
> Also documented in "Linux AIO Performance and Robustness for
> Enterprise
> Workloads" section 3.5:
>
> sendfile(fd, 0, 2GB, fd2) = 8192,
> tells readahead about up to 128KB of the read
> sendfile(fd, 8192, 2GB - 8192, fd2) = 8192,
> tells readahead about 8KB - 132KB of the read
> sendfile(fd, 16384, 2GB - 16384, fd2) = 8192,
> tells readahead about 16KB-140KB of the read
>...
> This confuses the readahead logic about the I/O pattern which
> appears
> to be 0-128K, 8K-132K, 16K-140K instead of clear sequentiality
> from
> 0-2GB that is really appropriate.
>
> Retry based AIO shares the same read pattern and readahead problem.
> In this case, simply disabling readahead on restarted aio is not a
> good option:
> we still need to call into readahead in the rare case of (req_size >
> ra_max).
The solution you proposed seems kludgy to me. If you determine that the
its a restarted aio, then start reading from where readahead had left
reading from earlier. To me a simple fix is:
- if (unlikely(aio_restarted()))
- next_index = last_index; /* Avoid repeat readahead */
+ if (unlikely(aio_restarted()))
+ next_index = min(prev_index+1, last_index);
No?
RP
>
> Signed-off-by: Fengguang Wu <[EMAIL PROTECTED]>
> ---
> mm/filemap.c |3 ---
> mm/readahead.c |9 +
> 2 files changed, 9 insertions(+), 3 deletions(-)
>
> --- linux-2.6.20-rc6-mm3.orig/mm/readahead.c
> +++ linux-2.6.20-rc6-mm3/mm/readahead.c
> @@ -581,6 +581,15 @@ page_cache_readahead(struct address_spac
> int sequential;
>
> /*
> +* A previous read request is partially completed,
> +* causing the retried/continued read calls into us
> prematurely.
> +*/
> + if (ra->start < offset &&
> + offset < ra->prev_page &&
> +ra->prev_page < ra->ahead_start +
> ra->ahead_size)
> + goto out;
> +
> + /*
> * We avoid doing extra work and bogusly perturbing the
> readahead
> * window expansion logic.
> */
> --- linux-2.6.20-rc6-mm3.orig/mm/filemap.c
> +++ linux-2.6.20-rc6-mm3/mm/filemap.c
> @@ -915,9 +915,6 @@ void do_generic_mapping_read(struct addr
> if (!isize)
> goto out;
>
> - if (unlikely(aio_restarted()))
> - next_index = last_index; /* Avoid repeat readahead */
> -
> end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
> for (;;) {
> struct page *page;
>
-
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Re: [PATCH -mm] readahead: partial sendfile fix
On Sat, 2007-02-10 at 09:40 +0800, Fengguang Wu wrote:
Enable readahead to handle partially done read requests, e.g.
sendfile(188, 1921, [1478592], 19553028) = 37440
sendfile(188, 1921, [1516032], 19515588) = 28800
sendfile(188, 1921, [1544832], 19486788) = 37440
sendfile(188, 1921, [1582272], 19449348) = 14400
sendfile(188, 1921, [1596672], 19434948) = 37440
sendfile(188, 1921, [1634112], 19397508) = 37440
In the above strace log,
- some lighttpd is doing _sequential_ reading
- every sendfile() returns with only _partial_ work done
page_cache_readahead() expects that if it returns @next_index, it will
be
called exactly at @next_index next time. That's not true here. So the
pattern
will be falsely recognized as a random read trace.
Also documented in Linux AIO Performance and Robustness for
Enterprise
Workloads section 3.5:
sendfile(fd, 0, 2GB, fd2) = 8192,
tells readahead about up to 128KB of the read
sendfile(fd, 8192, 2GB - 8192, fd2) = 8192,
tells readahead about 8KB - 132KB of the read
sendfile(fd, 16384, 2GB - 16384, fd2) = 8192,
tells readahead about 16KB-140KB of the read
...
This confuses the readahead logic about the I/O pattern which
appears
to be 0-128K, 8K-132K, 16K-140K instead of clear sequentiality
from
0-2GB that is really appropriate.
Retry based AIO shares the same read pattern and readahead problem.
In this case, simply disabling readahead on restarted aio is not a
good option:
we still need to call into readahead in the rare case of (req_size
ra_max).
The solution you proposed seems kludgy to me. If you determine that the
its a restarted aio, then start reading from where readahead had left
reading from earlier. To me a simple fix is:
- if (unlikely(aio_restarted()))
- next_index = last_index; /* Avoid repeat readahead */
+ if (unlikely(aio_restarted()))
+ next_index = min(prev_index+1, last_index);
No?
RP
Signed-off-by: Fengguang Wu [EMAIL PROTECTED]
---
mm/filemap.c |3 ---
mm/readahead.c |9 +
2 files changed, 9 insertions(+), 3 deletions(-)
--- linux-2.6.20-rc6-mm3.orig/mm/readahead.c
+++ linux-2.6.20-rc6-mm3/mm/readahead.c
@@ -581,6 +581,15 @@ page_cache_readahead(struct address_spac
int sequential;
/*
+* A previous read request is partially completed,
+* causing the retried/continued read calls into us
prematurely.
+*/
+ if (ra-start offset
+ offset ra-prev_page
+ra-prev_page ra-ahead_start +
ra-ahead_size)
+ goto out;
+
+ /*
* We avoid doing extra work and bogusly perturbing the
readahead
* window expansion logic.
*/
--- linux-2.6.20-rc6-mm3.orig/mm/filemap.c
+++ linux-2.6.20-rc6-mm3/mm/filemap.c
@@ -915,9 +915,6 @@ void do_generic_mapping_read(struct addr
if (!isize)
goto out;
- if (unlikely(aio_restarted()))
- next_index = last_index; /* Avoid repeat readahead */
-
end_index = (isize - 1) PAGE_CACHE_SHIFT;
for (;;) {
struct page *page;
-
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the body of a message to [EMAIL PROTECTED]
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Please read the FAQ at http://www.tux.org/lkml/
[PATCH -mm] readahead: partial sendfile fix
Enable readahead to handle partially done read requests, e.g.
sendfile(188, 1921, [1478592], 19553028) = 37440
sendfile(188, 1921, [1516032], 19515588) = 28800
sendfile(188, 1921, [1544832], 19486788) = 37440
sendfile(188, 1921, [1582272], 19449348) = 14400
sendfile(188, 1921, [1596672], 19434948) = 37440
sendfile(188, 1921, [1634112], 19397508) = 37440
In the above strace log,
- some lighttpd is doing _sequential_ reading
- every sendfile() returns with only _partial_ work done
page_cache_readahead() expects that if it returns @next_index, it will be
called exactly at @next_index next time. That's not true here. So the pattern
will be falsely recognized as a random read trace.
Also documented in "Linux AIO Performance and Robustness for Enterprise
Workloads" section 3.5:
sendfile(fd, 0, 2GB, fd2) = 8192,
tells readahead about up to 128KB of the read
sendfile(fd, 8192, 2GB - 8192, fd2) = 8192,
tells readahead about 8KB - 132KB of the read
sendfile(fd, 16384, 2GB - 16384, fd2) = 8192,
tells readahead about 16KB-140KB of the read
...
This confuses the readahead logic about the I/O pattern which appears
to be 0-128K, 8K-132K, 16K-140K instead of clear sequentiality from
0-2GB that is really appropriate.
Retry based AIO shares the same read pattern and readahead problem.
In this case, simply disabling readahead on restarted aio is not a good option:
we still need to call into readahead in the rare case of (req_size > ra_max).
Signed-off-by: Fengguang Wu <[EMAIL PROTECTED]>
---
mm/filemap.c |3 ---
mm/readahead.c |9 +
2 files changed, 9 insertions(+), 3 deletions(-)
--- linux-2.6.20-rc6-mm3.orig/mm/readahead.c
+++ linux-2.6.20-rc6-mm3/mm/readahead.c
@@ -581,6 +581,15 @@ page_cache_readahead(struct address_spac
int sequential;
/*
+* A previous read request is partially completed,
+* causing the retried/continued read calls into us prematurely.
+*/
+ if (ra->start < offset &&
+ offset < ra->prev_page &&
+ra->prev_page < ra->ahead_start +
ra->ahead_size)
+ goto out;
+
+ /*
* We avoid doing extra work and bogusly perturbing the readahead
* window expansion logic.
*/
--- linux-2.6.20-rc6-mm3.orig/mm/filemap.c
+++ linux-2.6.20-rc6-mm3/mm/filemap.c
@@ -915,9 +915,6 @@ void do_generic_mapping_read(struct addr
if (!isize)
goto out;
- if (unlikely(aio_restarted()))
- next_index = last_index; /* Avoid repeat readahead */
-
end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
for (;;) {
struct page *page;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH -mm] readahead: partial sendfile fix
Enable readahead to handle partially done read requests, e.g.
sendfile(188, 1921, [1478592], 19553028) = 37440
sendfile(188, 1921, [1516032], 19515588) = 28800
sendfile(188, 1921, [1544832], 19486788) = 37440
sendfile(188, 1921, [1582272], 19449348) = 14400
sendfile(188, 1921, [1596672], 19434948) = 37440
sendfile(188, 1921, [1634112], 19397508) = 37440
In the above strace log,
- some lighttpd is doing _sequential_ reading
- every sendfile() returns with only _partial_ work done
page_cache_readahead() expects that if it returns @next_index, it will be
called exactly at @next_index next time. That's not true here. So the pattern
will be falsely recognized as a random read trace.
Also documented in Linux AIO Performance and Robustness for Enterprise
Workloads section 3.5:
sendfile(fd, 0, 2GB, fd2) = 8192,
tells readahead about up to 128KB of the read
sendfile(fd, 8192, 2GB - 8192, fd2) = 8192,
tells readahead about 8KB - 132KB of the read
sendfile(fd, 16384, 2GB - 16384, fd2) = 8192,
tells readahead about 16KB-140KB of the read
...
This confuses the readahead logic about the I/O pattern which appears
to be 0-128K, 8K-132K, 16K-140K instead of clear sequentiality from
0-2GB that is really appropriate.
Retry based AIO shares the same read pattern and readahead problem.
In this case, simply disabling readahead on restarted aio is not a good option:
we still need to call into readahead in the rare case of (req_size ra_max).
Signed-off-by: Fengguang Wu [EMAIL PROTECTED]
---
mm/filemap.c |3 ---
mm/readahead.c |9 +
2 files changed, 9 insertions(+), 3 deletions(-)
--- linux-2.6.20-rc6-mm3.orig/mm/readahead.c
+++ linux-2.6.20-rc6-mm3/mm/readahead.c
@@ -581,6 +581,15 @@ page_cache_readahead(struct address_spac
int sequential;
/*
+* A previous read request is partially completed,
+* causing the retried/continued read calls into us prematurely.
+*/
+ if (ra-start offset
+ offset ra-prev_page
+ra-prev_page ra-ahead_start +
ra-ahead_size)
+ goto out;
+
+ /*
* We avoid doing extra work and bogusly perturbing the readahead
* window expansion logic.
*/
--- linux-2.6.20-rc6-mm3.orig/mm/filemap.c
+++ linux-2.6.20-rc6-mm3/mm/filemap.c
@@ -915,9 +915,6 @@ void do_generic_mapping_read(struct addr
if (!isize)
goto out;
- if (unlikely(aio_restarted()))
- next_index = last_index; /* Avoid repeat readahead */
-
end_index = (isize - 1) PAGE_CACHE_SHIFT;
for (;;) {
struct page *page;
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
