Re: [PATCH 1/10] shmem: replace page if mapping excludes its zone
From: KAMEZAWA Hiroyuki
Date: Mon May 14 2012 - 05:08:11 EST
(2012/05/12 20:59), Hugh Dickins wrote:
> The GMA500 GPU driver uses GEM shmem objects, but with a new twist:
> the backing RAM has to be below 4GB. Not a problem while the boards
> supported only 4GB: but now Intel's D2700MUD boards support 8GB, and
> their GMA3600 is managed by the GMA500 driver.
> shmem/tmpfs has never pretended to support hardware restrictions on
> the backing memory, but it might have appeared to do so before v3.1,
> and even now it works fine until a page is swapped out then back in.
> When read_cache_page_gfp() supplied a freshly allocated page for copy,
> that compensated for whatever choice might have been made by earlier
> swapin readahead; but swapoff was likely to destroy the illusion.
> We'd like to continue to support GMA500, so now add a new
> shmem_should_replace_page() check on the zone when about to move
> a page from swapcache to filecache (in swapin and swapoff cases),
> with shmem_replace_page() to allocate and substitute a suitable page
> (given gma500/gem.c's mapping_set_gfp_mask GFP_KERNEL | __GFP_DMA32).
> This does involve a minor extension to mem_cgroup_replace_page_cache()
> (the page may or may not have already been charged); and I've removed
> a comment and call to mem_cgroup_uncharge_cache_page(), which in fact
> is always a no-op while PageSwapCache.
> Also removed optimization of an unlikely path in shmem_getpage_gfp(),
> now that we need to check PageSwapCache more carefully (a racing caller
> might already have made the copy). And at one point shmem_unuse_inode()
> needs to use the hitherto private page_swapcount(), to guard against
> racing with inode eviction.
> It would make sense to extend shmem_should_replace_page(), to cover
> cpuset and NUMA mempolicy restrictions too, but set that aside for
> now: needs a cleanup of shmem mempolicy handling, and more testing,
> and ought to handle swap faults in do_swap_page() as well as shmem.
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
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