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Hello,

the time has come again for my monthly stress-testing of new kernels :-)
I installed 2.4.11-pre4 and ran it for a day. It was really strange for me to
see _no_ alloc failures at all, and that's why I gave it a closer look (alan
fooled me once by deleting the printk, which made the problem "disappear" too
:-). And here it is (from page_alloc.c):

rebalance:
page = balance_classzone(classzone, gfp_mask, order, &freed);
if (page)
return page;

zone = zonelist->zones;
if (likely(freed)) {
for (;;) {
zone_t *z = *(zone++);
if (!z)
break;

if (zone_free_pages(z, order) > z->pages_min) {
page = rmqueue(z, order);
if (page)
return page;
}
}
goto rebalance;
} else {
/*
* Check that no other task is been killed meanwhile,
* in such a case we can succeed the allocation.
*/
for (;;) {
zone_t *z = *(zone++);
if (!z)
break;

if (zone_free_pages(z, order) > z->pages_min) {
page = rmqueue(z, order);
if (page)
return page;
}
}

goto rebalance;
}

printk(KERN_NOTICE "%s __alloc_pages: %u-order allocation failed
(gfp=0x%x/%i) from %p\n",
current->comm, order, gfp_mask, !!(current->flags &
PF_MEMALLOC), __builtin_return_address(0));
/* my stuff :-) */
if (order==0)
show_trace(NULL);
return NULL;
}


As you can see I patched some more info output on certain alloc-failures. But
unfortunately I did not read the lines above - up to now. As you can see the
printk cannot be reached at all, because both if-cases jump to rebalance - not
matter how comes.
When I wrote the first version of this posting, I wrote: this looks like a
possible deadlock to me, because it cycles forever when no pages are found. I
proved myself right this time, because when I tried to send the mail and
started a CD burn at the background, the host froze. As you may remember the CD
burns always gave me alloc-failures during startup in earlier kernel versions.
So it is pretty obvious I reached the deadlock this time.
Another thing I would like to kindly ask: what is the difference in the two if
branches? As I cannot read really well (already proven in another thread :-), I
am very willing to accept any explanation on this code ;-)
If someone else has asked the whole thing before: shoot me.

Regards,
Stephan

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