2015-03-13 21:12 GMT+09:00 Roman Pen <r.peniaev@xxxxxxxxx>: > In original implementation of vm_map_ram made by Nick Piggin there were two > bitmaps: alloc_map and dirty_map. None of them were used as supposed to be: > finding a suitable free hole for next allocation in block. vm_map_ram allocates > space sequentially in block and on free call marks pages as dirty, so freed > space can't be reused anymore. > > Actually would be very interesting to know the real meaning of those bitmaps, > maybe implementation was incomplete, etc. > > But long time ago Zhang Yanfei removed alloc_map by these two commits: > > mm/vmalloc.c: remove dead code in vb_alloc > 3fcd76e8028e0be37b02a2002b4f56755daeda06 > mm/vmalloc.c: remove alloc_map from vmap_block > b8e748b6c32999f221ea4786557b8e7e6c4e4e7a > > In current patch I replaced dirty_map with two range variables: dirty min and > max. These variables store minimum and maximum position of dirty space in a > block, since we need only to know the dirty range, not exact position of dirty > pages. > > Why it was made? Several reasons: at first glance it seems that vm_map_ram > allocator concerns about fragmentation thus it uses bitmaps for finding free > hole, but it is not true. To avoid complexity seems it is better to use > something simple, like min or max range values. Secondly, code also becomes > simpler, without iteration over bitmap, just comparing values in min and max > macros. Thirdly, bitmap occupies up to 1024 bits (4MB is a max size of a > block). Here I replaced the whole bitmap with two longs. > > Finally vm_unmap_aliases should be slightly faster and the whole vmap_block > structure occupies less memory. > > Signed-off-by: Roman Pen <r.peniaev@xxxxxxxxx> > Cc: Nick Piggin <npiggin@xxxxxxxxx> > Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: WANG Chao <chaowang@xxxxxxxxxx> > Cc: Fabian Frederick <fabf@xxxxxxxxx> > Cc: Christoph Lameter <cl@xxxxxxxxx> > Cc: Gioh Kim <gioh.kim@xxxxxxx> > Cc: Rob Jones <rob.jones@xxxxxxxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx Acked-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>