linux-kernel - Re: [PATCH v2 2/3] move ClearPageReclaim

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Date:	Mon, 29 Nov 2010 16:26:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ben Gamari <bgamari.foss@...il.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH v2 2/3] move ClearPageReclaim

On Mon, Nov 29, 2010 at 04:16:01PM +0800, Minchan Kim wrote:
> On Mon, Nov 29, 2010 at 4:29 PM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> > On Sun, Nov 28, 2010 at 11:02:56PM +0800, Minchan Kim wrote:
> >> fe3cba17 added ClearPageReclaim into clear_page_dirty_for_io for
> >> preventing fast reclaiming readahead marker page.
> >>
> >> In this series, PG_reclaim is used by invalidated page, too.
> >> If VM find the page is invalidated and it's dirty, it sets PG_reclaim
> >> to reclaim asap. Then, when the dirty page will be writeback,
> >> clear_page_dirty_for_io will clear PG_reclaim unconditionally.
> >> It disturbs this serie's goal.
> >>
> >> I think it's okay to clear PG_readahead when the page is dirty, not
> >> writeback time. So this patch moves ClearPageReadahead.
> >> This patch needs Wu's opinion.
> >
> > It's a safe change. The possibility and consequence of races are both
> > small enough. However the patch could be simplified as follows?
> 
> If all of file systems use it, I don't mind it.
> Do all of filesystems use it when the page is dirtied?
> I was not sure it.(It's why I added Cc. :)
> If it doesn't have a problem, I hope so.

Please double check, but here is my findings:

__set_page_dirty_buffers() is called by several fs' ->set_page_dirty()
which are all called by set_page_dirty().

set_page_dirty_lock() will call set_page_dirty().

__set_page_dirty_no_writeback(): it have no connection to
end_page_writeback(), so no need to set PG_reclaim.

Thanks,
Fengguang


> > --- linux-next.orig/mm/page-writeback.c 2010-11-29 15:14:54.000000000 +0800
> > +++ linux-next/mm/page-writeback.c      2010-11-29 15:15:02.000000000 +0800
> > @@ -1330,6 +1330,7 @@ int set_page_dirty(struct page *page)
> >  {
> >        struct address_space *mapping = page_mapping(page);
> >
> > +       ClearPageReclaim(page);
> >        if (likely(mapping)) {
> >                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
> >  #ifdef CONFIG_BLOCK
> > @@ -1387,7 +1388,6 @@ int clear_page_dirty_for_io(struct page
> >
> >        BUG_ON(!PageLocked(page));
> >
> > -       ClearPageReclaim(page);
> >        if (mapping && mapping_cap_account_dirty(mapping)) {
> >                /*
> >                 * Yes, Virginia, this is indeed insane.
> >
> 
> 
> 
> -- 
> Kind regards,
> Minchan Kim
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