• Hugh Dickins's avatar
    shmem: replace page if mapping excludes its zone · bde05d1c
    Hugh Dickins authored
    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: default avatarHugh Dickins <hughd@google.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Cc: Stephane Marchesin <marcheu@chromium.org>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Dave Airlie <airlied@gmail.com>
    Cc: Daniel Vetter <daniel@ffwll.ch>
    Cc: Rob Clark <rob.clark@linaro.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    bde05d1c
shmem.c 69.4 KB