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Date: Mon, 30 Jan 2012 11:15:22 +0000 From: Mel Gorman <mel@....ul.ie> To: Marek Szyprowski <m.szyprowski@...sung.com> Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org, linux-mm@...ck.org, linaro-mm-sig@...ts.linaro.org, Michal Nazarewicz <mina86@...a86.com>, Kyungmin Park <kyungmin.park@...sung.com>, Russell King <linux@....linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Daniel Walker <dwalker@...eaurora.org>, Arnd Bergmann <arnd@...db.de>, Jesse Barker <jesse.barker@...aro.org>, Jonathan Corbet <corbet@....net>, Shariq Hasnain <shariq.hasnain@...aro.org>, Chunsang Jeong <chunsang.jeong@...aro.org>, Dave Hansen <dave@...ux.vnet.ibm.com>, Benjamin Gaignard <benjamin.gaignard@...aro.org> Subject: Re: [PATCH 02/15] mm: page_alloc: update migrate type of pages on pcp when isolating On Thu, Jan 26, 2012 at 10:00:44AM +0100, Marek Szyprowski wrote: > From: Michal Nazarewicz <mina86@...a86.com> > > This commit changes set_migratetype_isolate() so that it updates > migrate type of pages on pcp list which is saved in their > page_private. > > Signed-off-by: Michal Nazarewicz <mina86@...a86.com> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com> > --- > include/linux/page-isolation.h | 6 ++++++ > mm/page_alloc.c | 1 + > mm/page_isolation.c | 24 ++++++++++++++++++++++++ > 3 files changed, 31 insertions(+), 0 deletions(-) > > diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h > index 051c1b1..8c02c2b 100644 > --- a/include/linux/page-isolation.h > +++ b/include/linux/page-isolation.h > @@ -27,6 +27,12 @@ extern int > test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn); > > /* > + * Check all pages in pageblock, find the ones on pcp list, and set > + * their page_private to MIGRATE_ISOLATE. > + */ > +extern void update_pcp_isolate_block(unsigned long pfn); > + > +/* > * Internal funcs.Changes pageblock's migrate type. > * Please use make_pagetype_isolated()/make_pagetype_movable(). > */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e1c5656..70709e7 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5465,6 +5465,7 @@ out: > if (!ret) { > set_pageblock_migratetype(page, MIGRATE_ISOLATE); > move_freepages_block(zone, page, MIGRATE_ISOLATE); > + update_pcp_isolate_block(pfn); > } > > spin_unlock_irqrestore(&zone->lock, flags); > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 4ae42bb..9ea2f6e 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -139,3 +139,27 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn) > spin_unlock_irqrestore(&zone->lock, flags); > return ret ? 0 : -EBUSY; > } > + > +/* must hold zone->lock */ > +void update_pcp_isolate_block(unsigned long pfn) > +{ > + unsigned long end_pfn = pfn + pageblock_nr_pages; > + struct page *page; > + > + while (pfn < end_pfn) { > + if (!pfn_valid_within(pfn)) { > + ++pfn; > + continue; > + } > + There is a potential problem here that you need to be aware of. set_pageblock_migratetype() is called from start_isolate_page_range(). I do not think there is a guarantee that pfn + pageblock_nr_pages is not in a different block of MAX_ORDER_NR_PAGES. If that is right then your options are to add a check like this; if ((pfn & (MAX_ORDER_NR_PAGES - 1)) == 0 && !pfn_valid(pfn)) break; or else ensure that end_pfn is always MAX_ORDER_NR_PAGES aligned and in the same block as pfn and relying on the caller to have called pfn_valid. > + page = pfn_to_page(pfn); > + if (PageBuddy(page)) { > + pfn += 1 << page_order(page); > + } else if (page_count(page) == 0) { > + set_page_private(page, MIGRATE_ISOLATE); > + ++pfn; This is dangerous for two reasons. If the page_count is 0, it could be because the page is in the process of being freed and is not necessarily on the per-cpu lists yet and you cannot be sure if the contents of page->private are important. Second, there is nothing to prevent another CPU allocating this page from its per-cpu list while the private field is getting updated from here which might lead to some interesting races. I recognise that what you are trying to do is respond to Gilad's request that you really check if an IPI here is necessary. I think what you need to do is check if a page with a count of 0 is encountered and if it is, then a draining of the per-cpu lists is necessary. To address Gilad's concerns, be sure to only this this once per attempt at CMA rather than for every page encountered with a count of 0 to avoid a storm of IPIs. > + } else { > + ++pfn; > + } > + } > +} -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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