Sorry for the slow reply, but my shell account is broken and I had to
post from home.
On Nov 10, 2008, at 10:24 AM, Ilya Yanok wrote:
This patch adds support for 256K pages on PPC 44x along with
some hacks needed for this.
This description is insufficient, it describes neither the hacks nor
why they are required.
Ok. Actually there is only one hack -- increasing kernel stack size. We
do this because with 256K pages we get division by zero in
kernel/fork.c:
/*
* The default maximum number of threads is set to a safe
* value: the thread structures can take up at most half
* of memory.
*/
max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
so setting THREAD_SIZE to bigger value we can avoid this. I don't think
it's very clean solution but at least we stay powerpc-specific.
And why is keeping a line of code intact, which doesn't even match its
comment, by creating a hack workaround that increases memory
consumption, that is triggered by enabling an option that already
increases memory pressure, just to stay architecture specific anything
like sanity?
No. Submit a patch to address the division by zero instead.
Btw, I did some research for you (all are from torvalds/old-2.6-bkcvs,
and the last patch has been edited for relevance along with one of
the descriptions):
v2.6.10-rc2-g63f96a6
commit 63f96a6d9c1a54875f3bd07a6337993bc5180ecb
Author: torvalds <torvalds>
Commit: torvalds <torvalds>
Merge bk://linux-mtd.bkbits.net/mtd-bugsonly-2.6
into ppc970.osdl.org:/home/torvalds/v2.6/linux
2004/11/16 17:29:15-08:00 dhowells
[PATCH] Fork fix fix
The attached patch fixes the fork fix to avoid the divide-by-zero
error I'd
previously fixed, but without using any sort of conditional.
Signed-off-by: David Howells <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
...
BKrev: 419aaa45h5IsCw4CAYMVTOWK9oVaBA
diff --git a/kernel/fork.c b/kernel/fork.c
index f5fba87..f157ad6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -118,10 +118,7 @@ void __init fork_init(unsigned long mempages)
* value: the thread structures can take up at most half
* of memory.
*/
- if (THREAD_SIZE >= PAGE_SIZE)
- max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 8;
- else
- max_threads = mempages / 8;
+ max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
/*
* we need to allow at least 20 threads to boot a system
v2.6.10-rc1-g368b064
commit 368b06415c11e286f6ab3fe7c52bdd5b9b6f3008
Author: dhowells <dhowells>
Commit: dhowells <dhowells>
[PATCH] fix page size assumption in fork()
The attached patch fixes fork to get rid of the assumption that
THREAD_SIZE
>= PAGE_SIZE (on the FR-V the smallest available page size is 16KB).
Signed-Off-By: David Howells <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
BKrev: 4193db17ZJRaaVNEGezHMBUmByER4A
diff --git a/kernel/fork.c b/kernel/fork.c
index eb689d9..f5fba87 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -118,7 +118,11 @@ void __init fork_init(unsigned long mempages)
* value: the thread structures can take up at most half
* of memory.
*/
- max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 8;
+ if (THREAD_SIZE >= PAGE_SIZE)
+ max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 8;
+ else
+ max_threads = mempages / 8;
+
/*
* we need to allow at least 20 threads to boot a system
*/
v2.4.0-g4214e42
commit 4214e42f96d4051cb77b1b7c2b041715db84ffd9
Author: torvalds <torvalds>
Commit: torvalds <torvalds>
v2.4.9.11 -> v2.4.9.12
- Alan Cox: much more merging
- Pete Zaitcev: ymfpci race fixes
- Andrea Arkangeli: VM race fix and OOM tweak.
- Arjan Van de Ven: merge RH kernel fixes
- Andi Kleen: use more readable 'likely()/unlikely()' instead of
__builtin_expect()
- Keith Owens: fix 64-bit ELF types
- Gerd Knorr: mark more broken PCI bridges, update btaudio driver
- Paul Mackerras: powermac driver update
- me: clean up PTRACE_DETACH to use common infrastructure
BKrev: 3c603e338Tv2BTX9tkeBFGWLdI-r4Q
diff --git a/kernel/fork.c b/kernel/fork.c
index 9179e23..91aeda9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -72,7 +72,7 @@ void __init fork_init(unsigned long mempages)
* value: the thread structures can take up at most half
* of memory.
*/
- max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 16;
+ max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 8;
init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
v2.4.0-gcaeb6d6
commit caeb6d68179ecd9dfeac8fa17daa7150163fa318
Author: torvalds <torvalds>
Commit: torvalds <torvalds>
v2.4.9.10 -> v2.4.9.11
- Neil Brown: md cleanups/fixes
- Andrew Morton: console locking merge
- Andrea Arkangeli: major VM merge
BKrev: 3c603e2fnBNvsVsBbJrGD3fFs4xTFg
diff --git a/kernel/fork.c b/kernel/fork.c
index ebfbf2b..9179e23 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -72,7 +72,7 @@ void __init fork_init(unsigned long mempages)
* value: the thread structures can take up at most half
* of memory.
*/
- max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 2;
+ max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 16;
init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
So the comment has been wrong since 2.4.9.11, and has been changed
several times since then. It can be changed. And if you fix the
comment you might even get bonus points. Thinking about it though,
the minimum divide should be at least 2 (a partial page for a stack and
a page for a flat or omagic binary).
#ifdef CONFIG_PTE_64BIT
typedef unsigned long long pte_basic_t;
+#ifdef CONFIG_PPC_256K_PAGES
+#define PTE_SHIFT (PAGE_SHIFT - 7)
This seems to be missing the comment on how many ptes are actually in
the page that are in the other if and else cases.
Ok. I'll fix this. Actually it's another hack: we don't use full page
for PTE table because we need to reserve something for PGD
I don't understand "we need to reserve something for PGD". Do you
mean that you would not require a second page for the PGD because the
full pagetable could fit in one page? My first reaction was to say
then create pgtable-nopgd.h like the other two. The page walkers
support this with the advent of gigantic pages. Then I realized that
might not be optimal: while the page table might fit in one page, it
would mean you always allocate the pte space to cover the full address
space. Even if your processes spread out over the 3G of address space
allocated to them (32 bit kernel), you will allocate space for 4G,
wasting 1/4 of the pte space.
That does imply you want to allocate the pte page from a slab instead
of pgalloc. Is that covered?
milton
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