netdev - Re: lockless pagecache Cassini regression

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Message-Id: <20080104.035831.52071724.davem@davemloft.net>
Date:	Fri, 04 Jan 2008 03:58:31 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	npiggin@...e.de
Cc:	netdev@...r.kernel.org
Subject: Re: lockless pagecache Cassini regression

From: Nick Piggin <npiggin@...e.de>
Date: Fri, 4 Jan 2008 12:33:52 +0100

> Just for interest, the lockless pagecache actually makes
> page->_count unstable for all pages that _have ever_ been pagecache
> pages (since the last quiescent rcu state, anyway). Basically, it
> looks up and takes a ref on the struct page without ever having a
> prior pin or reference on that page. It can do this because it knows
> the struct page won't actually get freed. After taking the ref, it
> rechecks that it has got the right page...

Ok, I understand the needs now.

I think the way the drivers/net/niu.c driver handles things
would work better.  It only performs get_page(), atomic
increments on compound_head(page)->_count, and __free_page().
Is that all legal with the lockless pagecache?

If so I can likely rework the Cassini page management to
behave similarly.

> Acked-by: Nick Piggin <npiggin@...e.de>

Thanks for reviewing.
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