Re: why are some low-level MM routines being exported?

["Jörn Engel" <joern@logfs.org>]

On Mon, 5 April 2010 09:59:18 +0900, Minchan Kim wrote:
> On Mon, Apr 5, 2010 at 4:55 AM, JA?rn Engel <joern@logfs.org> wrote:
> > On Mon, 5 April 2010 01:21:52 +0900, Minchan Kim wrote:
> >> >
> >> Until now, other file system don't need it.
> >> Why do you need?
> >
> > To avoid deadlocks. A You tell logfs to write out some locked page, logfs
> > determines that it needs to run garbage collection first. A Garbage
> > collection can read any page. A If it called find_or_create_page() for
> > the locked page, you have a deadlock.
> 
> Could you do it with add_to_page_cache and pagevec_lru_add_file?

Maybe.  But how would that be an improvement?

As I see it, logfs needs a variant of find_or_create_page() that does
not block on any pages waiting for logfs GC.  Currently that variant
lives under fs/logfs/ and uses add_to_page_cache_lru().  If there are
valid reasons against exporting add_to_page_cache_lru(), the right
solution is to move the logfs variant to mm/, not to rewrite it.

If you want to change the implementation from using
add_to_page_cache_lru() to using add_to_page_cache() and
pagevec_lru_add_file(), then you should have a better reason than not
exporting add_to_page_cache_lru().  If the new implementation was any
better, I would gladly take it.

JA?rn

-- 
Money can buy bandwidth, but latency is forever.
-- John R. Mashey

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