Hi Georg,
in addition to Norman's remarks I further investigated your issue
(mostly because the value 32769 which is 0x8001 puzzled me).
On 22.12.2015 14:00, Georg Guba wrote:
> This shows 0/32769 on the first print and 28672/32769 on the second
> which is exactly what you'd expect. Allocating 29 KiB with a 32 KiB
> quota, however, will throw a Quota_exceeded exception, still printing
> 0/32769 on the first print.
>
> It seems you need about 4 KiB of spare quota but I can't seem to find
> any doc on this. How much quota should I actually reserve for simple
> allocations like this and why isn't it simply the same as the actual
> allocation size? I'd like to avoid magic numbers and wasteful allocation
> if possible.
With the patch applied I get the following output on linux_x86.
[init -> test-printf] 0/0
[init -> test-printf] 0/32768
[init -> test-printf] 16384/32768
So it's 0x8000 indeed and I assume a typo on your side. But, the
actual question is: Why can't one use the final 4 KiB of the RAM
quota? The answer leads us to the implementation of
Ram_session_component in core, which dates back several years and
includes the following comment in Ram_session_component::alloc().
/*
* Check quota!
*
* In the worst case, we need to allocate a new slab block for the
* meta data of the dataspace to be created - therefore, we add
* the slab block size here.
*/
Unfortunately, this piece of code does not (and currently can't) use
the available bytes in the meta-data allocator but in the RAM session
itself. It is remnant of the ongoing process of decoupling RAM
allocations from meta-data handling.
Thanks for sharing your findings, we'll address the issue with
https://github.com/genodelabs/genode/issues/1831
For now, the last 4 KiB of the RAM session quota are beyond reach,
sorry.
Regards
--
Christian Helmuth
Genode Labs
http://www.genode-labs.com/ · http://genode.org/
https://twitter.com/GenodeLabs · /ˈdʒiː.nəʊd/
Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth
repos/base/run/printf.run | 1 +
repos/base/src/test/printf/main.cc | 21 +++++++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/repos/base/run/printf.run b/repos/base/run/printf.run
index 032d3f2..70e4df1 100644
--- a/repos/base/run/printf.run
+++ b/repos/base/run/printf.run
@@ -6,6 +6,7 @@ install_config {
<config>
<parent-provides>
<service name="LOG"/>
+ <service name="RAM"/>
<service name="RM"/>
</parent-provides>
<default-route>
diff --git a/repos/base/src/test/printf/main.cc b/repos/base/src/test/printf/main.cc
index 51b617d..063e694 100644
--- a/repos/base/src/test/printf/main.cc
+++ b/repos/base/src/test/printf/main.cc
@@ -14,8 +14,29 @@
#include <base/printf.h>
+
+#include <base/env.h>
+#include <ram_session/connection.h>
+
+static void test()
+{
+ using namespace Genode;
+
+ Ram_connection ram;
+ ram.ref_account(env()->ram_session_cap());
+ PLOG("%zu/%zu", ram.used(), ram.quota());
+
+ env()->ram_session()->transfer_quota(ram.cap(), 32*1024);
+ PLOG("%zu/%zu", ram.used(), ram.quota());
+
+ ram.alloc(16*1024);
+ PLOG("%zu/%zu", ram.used(), ram.quota());
+}
+
int main(int argc, char **argv)
{
+ test();
+
/* test that unsupported commands don't crash the printf parser */
Genode::printf("%#x %s\n", 0x38, "test 1");
Genode::printf("%#lx %s\n", 0x38L, "test 2");
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