Re: patch-2.4.10-pre1

Marcelo Tosatti
2001-08-27T21:46:23Z

On Mon, 27 Aug 2001, Linus Torvalds wrote:

>
> On Mon, 27 Aug 2001, Marcelo Tosatti wrote:
> >
> > There have been some reports of x-order allocation failures when you where
> > in Finland. They can be triggered by high IO stress on highmem machines.
> >
> > The following patch avoids that by allowing tasks allocating bounce memory
> > (lowmem) to block on low mem IO, thus applying more "IO pressure" to the
> > lowmem zone. (the lowmem zone is our "IOable memory" anyway, so...)
>
> I'd much rather set this up by splitting up __GFP_IO into two parts (ie
> __GFP_IO and __GFP_IO_BOUNCE), and avoiding have "negative" bits in the
> gfp_mask. That way the bits in gfp_mask always end up increasing things we
> can do, not ever decreasing them.
>
> Also, your test is really wrong:
>
> page->zone != &pgdat_list->node_zones[ZONE_HIGHMEM]
>
> is bogus and assumes MUCH too intimate knowledge of there being only one
> particular zone that is "highmem" (think NUMA machines where each node may
> have its own highmem setup). So it SHOULD be something along the lines of
>
> #ifdef CONFIG_HIGHMEM
> if (!(gfp_mask & __GFP_HIGHIO) && PageHighMem(page))
> return;
> #endif
>
> inside the write case of sync_page_buffers() (we can, and probably should,
> still _wait_ for highmem buffers - but whether we do it inside
> sync_page_buffers() or inside try_to_free_buffers() is probably mostly a
> matter of taste - I won't argue too much with your choice there).
>
> Other than that, the basic approach looks sane, I would just prefer for
> the testing and bits to be done more regularly.

Great. I really expected you to be grumpy about the implementation :)

Will implement the idea decently and send you the patch later.