Re: [RFC 0/7] Postphone reclaim laundry to write at high water marks

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2007-08-20 at 14:50 -0700, Christoph Lameter wrote:
> One of the problems with reclaim writeout is that it occurs when memory in a
> zone is low. A particular bad problem can occur if memory in a zone is
> already low and now the first page that we encounter during reclaim is dirty.
> So the writeout function is called without the filesystem or device having
> much of a reserve that would allow further allocations. Triggering writeout
> of dirty pages early does not improve the memory situation since the actual
> writeout of the page is a relatively long process. The call to writepage
> will therefore not improve the low memory situation but make it worse
> because extra memory may be needed to get the device to write the page.
> 
> This patchset fixes that issue by:
> 
> 1. First reclaiming non dirty pages. Dirty pages are deferred until reclaim
>    has reestablished the high marks. Then all the dirty pages (the laundry)
>    is written out.
> 
> 2. Reclaim is essentially complete during the writeout phase. So we remove
>    PF_MEMALLOC and allow recursive reclaim if we still run into trouble
>    during writeout.

This almost insta-OOMs with anonymous workloads.