Re: [PATCH 12/14] vmscan: Do not writeback pages in direct reclaim

[Christoph Hellwig]

On Tue, Jul 06, 2010 at 10:27:58PM +0200, Johannes Weiner wrote:
> It bypasses the fs.  On swapon, the blocks are resolved
> (mm/swapfile.c::setup_swap_extents) and then the writeout path uses
> bios directly (mm/page_io.c::swap_writepage).
> 
> (GFP_NOFS still includes __GFP_IO, so allows swapping)

Exactly.  Note that while the stack problems for swap writeout aren't
as bad as for filesystems as the whole allocator / extent map footprint
is missing it might still be an issue.  We still splice the whole block
I/O stack footprint over a random stack that might be filled up a lot.
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