Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [RFC 6/8] In order putback lru core | Date | Mon, 9 May 2011 12:21:11 +0900 (JST) |
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> On Sun, May 1, 2011 at 10:47 PM, KOSAKI Motohiro > <kosaki.motohiro@jp.fujitsu.com> wrote: > >> > +/* This structure is used for keeping LRU ordering of isolated page */ > >> > +struct pages_lru { > >> > + struct page *page; /* isolated page */ > >> > + struct page *prev_page; /* previous page of isolate page as LRU order */ > >> > + struct page *next_page; /* next page of isolate page as LRU order */ > >> > + struct list_head lru; > >> > +}; > >> > /* > >> > >> So this thing has to be allocated from somewhere. We can't put it > >> on the stack as we're already in danger there so we must be using > >> kmalloc. In the reclaim paths, this should be avoided obviously. > >> For compaction, we might hurt the compaction success rates if pages > >> are pinned with control structures. It's something to be wary of. > >> > >> At LSF/MM, I stated a preference for swapping the source and > >> destination pages in the LRU. This unfortunately means that the LRU > >> now contains a page in the process of being migrated to and the backout > >> paths for migration failure become a lot more complex. Reclaim should > >> be ok as it'll should fail to lock the page and recycle it in the list. > >> This avoids allocations but I freely admit that I'm not in the position > >> to implement such a thing right now :( > > > > I like swaping to fake page. one way pointer might become dangerous. vmscan can > > detect fake page and ignore it. > > > I guess it means swapping between migrated-from page and migrated-to page. > Right?
no. I was intend to use fake struct page. but this idea is also good to me.
> If so, migrated-from page is already removed from LRU list and > migrated-to page isn't LRU as it's page allocated newly so they don't > have any LRU information. How can we swap them? We need space keeps > LRU information before removing the page from LRU list. :(
pure fake struct page or preallocation migrated-to page?
> > Could you explain in detail about swapping if I miss something? > > About one way pointer, I think it's no problem. Worst case I imagine > is to put the page in head of LRU list. It means it's same issue now. > So it doesn't make worse than now. > > > > > ie, > > is_fake_page(page) > > { > > if (is_stack_addr((void*)page)) > > return true; > > return false; > > } > > > > Also, I like to use stack rather than kmalloc in compaction. > > > > Compaction is a procedure of reclaim. As you know, we had a problem > about using of stack during reclaim path. > I admit kmalloc-thing isn't good. > I will try to solve the issue as TODO.
It depend on stack consumption size. because we don't call pageout() from compaction path. It's big different from regular reclaim path.
> > Thanks for the review, KOSAKI.
Yeah, thank you for making very good patch!
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