• Rik van Riel's avatar
    mm: prevent kswapd from freeing excessive amounts of lowmem · 32a4330d
    Rik van Riel authored
    The current VM can get itself into trouble fairly easily on systems with a
    small ZONE_HIGHMEM, which is common on i686 computers with 1GB of memory.
    
    On one side, page_alloc() will allocate down to zone->pages_low, while on
    the other side, kswapd() and balance_pgdat() will try to free memory from
    every zone, until every zone has more free pages than zone->pages_high.
    
    Highmem can be filled up to zone->pages_low with page tables, ramfs,
    vmalloc allocations and other unswappable things quite easily and without
    many bad side effects, since we still have a huge ZONE_NORMAL to do future
    allocations from.
    
    However, as long as the number of free pages in the highmem zone is below
    zone->pages_high, kswapd will continue swapping things out from
    ZONE_NORMAL, too!
    
    Sami Farin managed to get his system into a stage where kswapd had freed
    about 700MB of low memory and was still "going strong".
    
    The attached patch will make kswapd stop paging out data from zones when
    there is more than enough memory free.  We do go above zone->pages_high in
    order to keep pressure between zones equal in normal circumstances, but the
    patch should prevent the kind of excesses that made Sami's computer totally
    unusable.
    Signed-off-by: default avatarRik van Riel <riel@redhat.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    32a4330d
vmscan.c 51.7 KB