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digitalmars.D - druntime's PAGESIZE

reply Denis Feklushkin <feklushkin.denis gmail.com> writes:
Hi!

Looks like some of these values are redundant:

src/rt/lifetime.d
31:        PAGESIZE = 4096,

src/gc/pooltable.d
181:    enum PAGESIZE = 4096;

src/gc/impl/conservative/gc.d
1133:{   PAGESIZE =    4096,

This is correct? Which ones are related to each other? Which ones 
can be freely changed so that nothing (silently) breaks?

On a small system these values ​​seems too high.
Oct 31 2020
next sibling parent reply IGotD- <nise nise.com> writes:
On Saturday, 31 October 2020 at 19:06:33 UTC, Denis Feklushkin 
wrote:

 Hi!

 Looks like some of these values are redundant:

 src/rt/lifetime.d
 31:        PAGESIZE = 4096,

 src/gc/pooltable.d
 181:    enum PAGESIZE = 4096;

 src/gc/impl/conservative/gc.d
 1133:{   PAGESIZE =    4096,

 This is correct? Which ones are related to each other? Which 
 ones can be freely changed so that nothing (silently) breaks?

 On a small system these values ​​seems too high.


Yes, this is particular bad and also this should OS configurable 
(there might be an OS that suddenly bumps the page size to let's 
say 16KB) and not part of the D memory management code but part 
of the OS specific configuration.

Another problem for small systems is that the GC seems to assume 
page aligned memory, typically received from mmap or 
VirtualAlloc, however on small system and using the malloc 
fallback this doesn't work well. This waste memory on small 
system.

This should be fixed.
Oct 31 2020
parent reply Patrick Schluter <Patrick.Schluter bbox.fr> writes:
On Saturday, 31 October 2020 at 19:18:08 UTC, IGotD- wrote:

 On Saturday, 31 October 2020 at 19:06:33 UTC, Denis Feklushkin 
 wrote:

 [...]


 Yes, this is particular bad and also this should OS 
 configurable (there might be an OS that suddenly bumps the page 
 size to let's say 16KB) and not part of the D memory management 
 code but part of the OS specific configuration.


SPARC has 8K pages. Ok SPARC is almost dead but still.
iOS also went full on bigger pages (16K afaicr).


 Another problem for small systems is that the GC seems to 
 assume page aligned memory, typically received from mmap or 
 VirtualAlloc, however on small system and using the malloc 
 fallback this doesn't work well. This waste memory on small 
 system.

 This should be fixed.


Yes.
Oct 31 2020
parent Jacob Carlborg <doob me.com> writes:
On 2020-10-31 20:54, Patrick Schluter wrote:


 iOS also went full on bigger pages (16K afaicr).


Yes, see my other reply.

-- 
/Jacob Carlborg
Nov 01 2020
prev sibling next sibling parent Mathias LANG <geod24 gmail.com> writes:
On Saturday, 31 October 2020 at 19:06:33 UTC, Denis Feklushkin 
wrote:

 Hi!

 Looks like some of these values are redundant:

 src/rt/lifetime.d
 31:        PAGESIZE = 4096,

 src/gc/pooltable.d
 181:    enum PAGESIZE = 4096;

 src/gc/impl/conservative/gc.d
 1133:{   PAGESIZE =    4096,

 This is correct? Which ones are related to each other? Which 
 ones can be freely changed so that nothing (silently) breaks?

 On a small system these values ​​seems too high.


I should probably come back and finalize 
https://github.com/dlang/druntime/pull/3074 then :)
Nov 01 2020
prev sibling parent Jacob Carlborg <doob me.com> writes:
On 2020-10-31 20:06, Denis Feklushkin wrote:


 Looks like some of these values are redundant:
 
 src/rt/lifetime.d
 31:        PAGESIZE = 4096,
 
 src/gc/pooltable.d
 181:    enum PAGESIZE = 4096;
 
 src/gc/impl/conservative/gc.d
 1133:{   PAGESIZE =    4096,
 
 This is correct? Which ones are related to each other? Which ones can be 
 freely changed so that nothing (silently) breaks?


These are not correct. When I ported D to iOS I had to deal with this. 
The page size on iOS (and derived platforms) is 16K. It did change it in 
a few places where it broke the unit tests (or otherwise failed). I 
added two new symbols to `pageSize` and `minimumPageSize` [1]. The 
difference is that `minimumPageSize` is a compile time known value and 
might not be correct. `pageSize` is a runtime value which is initialized 
early in the startup phase. It's always correct since it gets the page 
size from the OS. `minimumPageSize` is discouraged, we might remove it.

I did a search through druntime and Phobos for the value `4096` and it 
appears quite a lot. I don't know how many of these values have to match 
the page size (i.e. for correctness) how many of these should ideally 
match the page size (i.e. for performance) or how many of these refer to 
something else (or it won't matter for performance or correctness).

I fixed all the places that was required to get the unit tests in 
druntime and Phobos to pass. If that means we're all good (at least for 
correctness) or that we don't have enough unit test coverage, I don't know.

[1] 
https://github.com/dlang/druntime/blob/4d68a910d74b3156b350701c08a97cf587da887a/src/core/memory.d#L181-L250

-- 
/Jacob Carlborg
Nov 01 2020