working of balance_classzone()

Hi,

I was commenting the code of balance_classzone() and am stuck up
at some point. The code in question is:

	if (likely(__freed)) {
	/* pick from the last inserted so we're lifo */
		entry = local_pages->next;
		do {
		     tmp = list_entry(entry, struct page, list);
---->>		     if (tmp->index == order && memclass(page_zone(tmp), classzone)) {
				list_del(entry);
				current->nr_local_pages--;
				set_page_count(tmp, 1);
				page = tmp;
				.................


	According to the code of __free_pages_ok(), when we try to free

pages with PF_FREE_PAGES set (as is done in balance_classzone() before the call to try_to_free_pages()) only one block of pages of some order is added to the local_pages member of the current task. Also nr_local_pages is 1 if there is a block of pages else it is 0 (ie. being used as a flag).

[related code: local_freelist:

	           if (current->nr_local_pages)
	                goto back_local_freelist;]



	So the code in balance_classzone() looks very suspicious as it

is acting as if there were many blocks of free pages of different orders on the list and we are trying to get the block of the correct order and then freeing the rest in reverse order....

Since there is only one block, we can cut the code to just check
the order of that block, if its greater than our requirement, call rmqueue() else return NULL.

If i am missing something or u've not understood my doubt,
please let me know...

Bye,
Abhi.

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Bye,
Abhi.

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The code hereabouts has been marooned for many releases, somewhere in between what Andrea intended and what Linus wanted. You're right that there's a (harmless) mismatch between what __free_pages_ok is actually doing, and what balance_classzone is expecting it to do. But that should get sorted out when Andrea's further VM patches are merged into 2.4.20... (always seems to be around the next corner).

Hugh

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