[PATCH 1/2] pipe.7: Note change to default pipe size when soft limit is exceeded

[PATCH 1/2] pipe.7: Note change to default pipe size when soft limit is exceeded

[Kienan Stewart]

See upstream commit:

    commit 46c4c9d1beb7f5b4cec4dd90e7728720583ee348
    Author: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
    Date:   Thu Aug 5 10:40:47 2021 -0400

        pipe: increase minimum default pipe size to 2 pages

Signed-off-by: Kienan Stewart <kstewart@efficios.com>
---
 man/man7/pipe.7 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/man/man7/pipe.7 b/man/man7/pipe.7
index d1fad9974..c7f3fbb9e 100644
--- a/man/man7/pipe.7
+++ b/man/man7/pipe.7
@@ -223,6 +223,9 @@ So long as the total number of pages allocated to pipe buffers
 for this user is at this limit,
 individual pipes created by a user will be limited to one page,
 and attempts to increase a pipe's capacity will be denied.
+As of Linux 5.14 the default capacity of individual pipes created
+by a user is two pages instead. Users may reduce the pipe capacity
+below this default value.
 .IP
 When the value of this limit is zero, no soft limit is applied.
 The default value for this file is 16384,
-- 
2.45.2

[PATCH 2/2] pipe.7: Reference potential lower default in pipe capacity section

[Kienan Stewart]

The pipe capacity section makes no indication that the default
capacity of pipes may not be `16 * PAGE_SIZE` for users exceeding the
`pipe_user_pages_soft` limit.

Signed-off-by: Kienan Stewart <kstewart@efficios.com>
---
 man/man7/pipe.7 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/man/man7/pipe.7 b/man/man7/pipe.7
index c7f3fbb9e..3d853d27c 100644
--- a/man/man7/pipe.7
+++ b/man/man7/pipe.7
@@ -131,6 +131,9 @@ operations.
 See
 .BR fcntl (2)
 for more information.
+Since Linux 4.5, the default pipe capacity is lower than 16 pages when the
+.I pipe\-user\-pages\-soft
+limit is exceeded.
 .P
 The following
 .BR ioctl (2)
-- 
2.45.2

Re: [PATCH 2/2] pipe.7: Reference potential lower default in pipe capacity section

[Alejandro Colomar]

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Hi Kienan,

On Thu, Aug 29, 2024 at 11:43:04AM GMT, Kienan Stewart wrote:
> The pipe capacity section makes no indication that the default
> capacity of pipes may not be `16 * PAGE_SIZE` for users exceeding the
> `pipe_user_pages_soft` limit.
> 
> Signed-off-by: Kienan Stewart <kstewart@efficios.com>
> ---

Thanks for the patch!  I've applied it, with small tweaks to the commit
message.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=663202e816e27dbfb5fddfeb2b93a86919f69027>

Have a lovely day!
Alex

>  man/man7/pipe.7 | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/man/man7/pipe.7 b/man/man7/pipe.7
> index c7f3fbb9e..3d853d27c 100644
> --- a/man/man7/pipe.7
> +++ b/man/man7/pipe.7
> @@ -131,6 +131,9 @@ operations.
>  See
>  .BR fcntl (2)
>  for more information.
> +Since Linux 4.5, the default pipe capacity is lower than 16 pages when the
> +.I pipe\-user\-pages\-soft
> +limit is exceeded.
>  .P
>  The following
>  .BR ioctl (2)
> -- 
> 2.45.2
> 

-- 
<https://www.alejandro-colomar.es/>

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Re: [PATCH 1/2] pipe.7: Note change to default pipe size when soft limit is exceeded

[Alejandro Colomar]

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Hi Kienan,

On Thu, Aug 29, 2024 at 11:43:03AM GMT, Kienan Stewart wrote:
> See upstream commit:
> 
>     commit 46c4c9d1beb7f5b4cec4dd90e7728720583ee348
>     Author: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>

[CC += Alex Xu]

>     Date:   Thu Aug 5 10:40:47 2021 -0400
> 
>         pipe: increase minimum default pipe size to 2 pages
> 
> Signed-off-by: Kienan Stewart <kstewart@efficios.com>
> ---
>  man/man7/pipe.7 | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/man/man7/pipe.7 b/man/man7/pipe.7
> index d1fad9974..c7f3fbb9e 100644
> --- a/man/man7/pipe.7
> +++ b/man/man7/pipe.7
> @@ -223,6 +223,9 @@ So long as the total number of pages allocated to pipe buffers
>  for this user is at this limit,
>  individual pipes created by a user will be limited to one page,
>  and attempts to increase a pipe's capacity will be denied.
> +As of Linux 5.14 the default capacity of individual pipes created

I think it makes more sense to say "Since" rather than "As of".
"Since" more clearly says what happens in Linux 5.13 and Linux 5.15.

Also, this sentence doesn't seem to relate to the one-page limit
mentioned in this paragraph, which is only when the soft limit for the
number of pipes has been reached.  It seems to say that this limit is
the default limit of individual pipes, with no mention to the soft limit
of pipes.

And also, I would mention the current behavior first, and only as a note
the historic behavior, instead of first mentioning the historic behavior
and later the current one.

Instead of your proposal, I would do:

	-individual pipes created by a user will be limited to one page,
	+individual pipes created by a user will be
	+limited to two pages
	+(one page before Linux 5.14),
	 and attempts to increase a pipe's capacity will be denied.

Have a lovely day!
Alex

> +by a user is two pages instead. Users may reduce the pipe capacity
> +below this default value.
>  .IP
>  When the value of this limit is zero, no soft limit is applied.
>  The default value for this file is 16384,
> -- 
> 2.45.2
> 
> 

-- 
<https://www.alejandro-colomar.es/>

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