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Date: Mon, 1 Aug 2011 01:21:13 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
Johannes Weiner <hannes@...xchg.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
Michal Hocko <mhocko@...e.cz>,
Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v4 06/10] migration: introudce migrate_ilru_pages
On Wed, Jul 27, 2011 at 01:13:57PM -0700, Andrew Morton wrote:
> On Mon, 4 Jul 2011 23:04:39 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
> > This patch defines new APIs to put back new page into old page's position as LRU order.
> > for LRU churning of compaction.
> >
> > The idea I suggested in LSF/MM is simple.
> >
> > ...
> >
> > +static bool same_lru(struct page *page, struct page *prev)
> > +{
> > + bool ret = false;
> > + if (!prev || !PageLRU(prev))
>
> Both parts of this test need explanations so readers can understand why
> they are here.
>
> > + goto out;
> > +
> > + if (unlikely(PageUnevictable(prev)))
>
> As does this.
Will do.
>
> > + goto out;
> > +
> > + if (page_lru_base_type(page) != page_lru_base_type(prev))
> > + goto out;
>
> This (and testing for PageLRU) is the only part of this function whcih
> is sufficiently obvious to leave undocumented.
>
> > + ret = true;
> > +out:
> > + return ret;
> > +}
> > +
> > +void putback_ilru_pages(struct inorder_lru *l)
> > +{
> > + struct zone *zone;
> > + struct page *page, *page2, *prev;
> > +
> > + list_for_each_ilru_entry_safe(page, page2, l, ilru) {
> > + ilru_list_del(page, l);
> > + dec_zone_page_state(page, NR_ISOLATED_ANON +
> > + page_is_file_cache(page));
> > + zone = page_zone(page);
> > + spin_lock_irq(&zone->lru_lock);
> > + prev = page->ilru.prev_page;
> > + if (same_lru(page, prev)) {
> > + putback_page_to_lru(page, prev);
> > + spin_unlock_irq(&zone->lru_lock);
> > + put_page(page);
> > + } else {
> > + spin_unlock_irq(&zone->lru_lock);
> > + putback_lru_page(page);
> > + }
> > + }
> > +}
>
> This function takes lru_lock at lest once per page, up to twice per
> page. The spinlocking frequency here could be optimised tremendously.
Yes. Mel is pointed out and I sent a [8/10] patch about it.
>
> The trick of hanging onto zone->lru_lock is the zone didn't change gets
> hard if we want to do a put_page() inside the loop.
>
> We have functions "putback_page_to_lru()" and "putback_lru_page()".
> Ugh. Can we think of better naming?
Yes. The name is bad but It's disappeared at [8/10].
>
> Does this function even need to exist if CONFIG_MIGRATION=n?
Of course, NOT.
I will nullify it in case of no migration.
>
> > +/*
> > * Restore a potential migration pte to a working pte entry
> > */
> >
> > ...
> >
> > +void __put_ilru_pages(struct page *page, struct page *newpage,
> > + struct inorder_lru *prev_lru, struct inorder_lru *ihead)
>
> The function name leaves me wondering where we put the pages, and
> there's no documentation telling me.
It seems remained thing to me is to add documentation.
I will add documentation in next version.
>
> > +{
> > + struct page *prev_page;
> > + struct zone *zone;
> > + prev_page = page->ilru.prev_page;
> > + /*
> > + * A page that has been migrated has all references
> > + * removed and will be freed. A page that has not been
> > + * migrated will have kepts its references and be
> > + * restored.
> > + */
> > + ilru_list_del(page, prev_lru);
> > + dec_zone_page_state(page, NR_ISOLATED_ANON +
> > + page_is_file_cache(page));
> > +
> > + /*
> > + * Move the new page to the LRU. If migration was not successful
> > + * then this will free the page.
> > + */
> > + zone = page_zone(newpage);
> > + spin_lock_irq(&zone->lru_lock);
> > + if (same_lru(page, prev_page)) {
> > + putback_page_to_lru(newpage, prev_page);
> > + spin_unlock_irq(&zone->lru_lock);
> > + /*
> > + * The newpage replaced LRU position of old page and
> > + * old one would be freed. So let's adjust prev_page of pages
> > + * remained in inorder_lru list.
> > + */
> > + adjust_ilru_prev_page(ihead, page, newpage);
> > + put_page(newpage);
> > + } else {
> > + spin_unlock_irq(&zone->lru_lock);
> > + putback_lru_page(newpage);
> > + }
>
> The same spinlocking frequency issue.
>
> > + putback_lru_page(page);
> > +}
> > +
> >
> > ...
> >
> > +int migrate_ilru_pages(struct inorder_lru *ihead, new_page_t get_new_page,
> > + unsigned long private, bool offlining, bool sync)
> > +{
> > + int retry = 1;
> > + int nr_failed = 0;
> > + int pass = 0;
> > + struct page *page, *page2;
> > + struct inorder_lru *prev;
> > + int swapwrite = current->flags & PF_SWAPWRITE;
> > + int rc;
> > +
> > + if (!swapwrite)
> > + current->flags |= PF_SWAPWRITE;
> > +
> > + for (pass = 0; pass < 10 && retry; pass++) {
>
> That ten-passes thing was too ugly to live, and now it's breeding. Argh.
Personally, I hope we remove it.
I will consider it later version or as independent patch.
Thanks for the review, Andrew!
--
Kind regards,
Minchan Kim
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