Re: [PATCH v5 6/7] mm: Support address range reclaim

[Minchan Kim]

On Tue, May 21, 2013 at 05:33:32PM -0700, Andrew Morton wrote:
> On Thu,  9 May 2013 16:21:28 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> 
> > This patch adds address range reclaim of a process.
> > The requirement is following as,
> > 
> > Like webkit1, it uses a address space for handling multi tabs.
> > IOW, it uses *one* process model so all tabs shares address space
> > of the process. In such scenario, per-process reclaim is rather
> > coarse-grained so this patch supports more fine-grained reclaim
> > for being able to reclaim target address range of the process.
> > For reclaim target range, you should use following format.
> > 
> > 	echo [addr] [size-byte] > /proc/pid/reclaim
> > 
> > The addr should be page-aligned.
> > 
> > So now reclaim konb's interface is following as.
> > 
> > echo file > /proc/pid/reclaim
> > 	reclaim file-backed pages only
> > 
> > echo anon > /proc/pid/reclaim
> > 	reclaim anonymous pages only
> > 
> > echo all > /proc/pid/reclaim
> > 	reclaim all pages
> > 
> > echo 0x100000 8K > /proc/pid/reclaim
> > 	reclaim pages in (0x100000 - 0x102000)
> 
> This might be going a bit far.  The application itself can be modified
> to use fadvise/madvise/whatever to release unused pages and that's a
> better interface.

I agree. The webkit should be smarter and it's going on afaik but
let's think another usecase that makes snapshot image scenario
I mentioned in previous reply.

Admin should discard NOT-IMPORTANT pages without modifying application's
code.

In addition, maybe we need madvise(MADV_SWAPOUT_NOT_DONTNEED) for
anonymous pages if we don't have such feature.

> 
> Athough it's a bit of a pipe-dream, I do think we should encourage
> userspace to go this path, rather than providing ways for hacky admin
> tools to go poking around in /proc/pid/maps and whacking apps
> externally.
> 
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-- 
Kind regards,
Minchan Kim
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