Re: Zoned CART

[Rahul Iyer <rni@andrew.cmu.edu>]

Hi Marcelo,

>I find it a very interesting idea to split the active list in two!  
>
>+#define EVICTED_ACTIVE                 1
>+#define EVICTED_LONGTERM       2
>+#define ACTIVE                 3
>+#define ACTIVE_LONGTERM                4
>
>You have different definitions using the same bit positions.
>Those values should be 1, 2, 4 and 8.
>  
>
Agreed! Dumb mistake.

>+#define EvictedActive(location)                location & EVICTED_ACTIVE
>+#define EvictedLongterm(location)      location & EVICTED_LONGTERM
>+#define Active(location)               location & ACTIVE
>+#define ActiveLongterm(location)       location & ACTIVE_LONGTERM
>
>(location  & xxxx) looks nicer.
>  
>
Will do this too...

>+struct non_res_list_node {
>+	struct list_head list;
>+	struct list_head hash;
>+	unsigned long mapping;
>+	unsigned long offset;
>+	unsigned long inode;
>+}; 
>
>+	node->offset = page->index;
>+	node->mapping = (unsigned long) page->mapping;
>+	node->inode = get_inode_num(page->mapping);
>
>You can compress these tree fields into a single one with a hash function.
>  
>
Yes, but then you would not be able to handle hash collisions. Are we 
prepared to give up this property?

>+/* The replace function. This function serches the active and longterm
>+lists and looks for a candidate for replacement. This function selects
>+the candidate and returns the corresponding structpage or returns
>+NULL in case no page can be freed. The *where argument is used to
>+indicate the parent list of the page so that, in case it cannot be
>+written back, it can be placed back on the correct list */ 
>+struct page *replace(struct zone *zone, int *where)
>
>+	list = list->next;
>+	while (list !=&zone->active_longterm) {
>+		page = list_entry(list, struct page, lru);
>+
>+		if (!PageReferenced(page))
>+			break;
>+		
>+		ClearPageReferenced(page);
>+		del_page_from_active_longterm(zone, page);
>+		add_page_to_active_list_tail(zone, page);
>
>This sounds odd. If a page is referenced you remove it from the longterm list
>"unpromoting" it to the active list? Shouldnt be the other way around?
>
>  
>
I'll re-check this in the CART paper. 

Currently I'm out of town, so i'll get this patch in with the 
corrections as soon as i get back.
Thanks
Rahul

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