ffs: Limit bulk transfer size to page size (4096 bytes)

ffs: Limit bulk transfer size to page size (4096 bytes)

This commit it intended to fix page allocation failures
in kernel due to ffs trying to allocate continuous memory
of length specified by userspace.

[ 2452.765000] sdbd: page allocation failure: order:6, mode:0x24040c0
[ 2452.770000] CPU: 2 PID: 6253 Comm: sdbd Not tainted 4.4.71-00002-g4b213b7 #130
[ 2452.780000] Hardware name: s5p4418
[ 2452.780000] [<c001964c>] (unwind_backtrace) from [<c0014ec8>] (show_stack+0x20/0x24)
[ 2452.790000] [<c0014ec8>] (show_stack) from [<c03516d8>] (dump_stack+0x80/0x94)
[ 2452.795000] [<c03516d8>] (dump_stack) from [<c0139738>] (warn_alloc_failed+0xf0/0x130)
[ 2452.805000] [<c0139738>] (warn_alloc_failed) from [<c013cef0>] (__alloc_pages_nodemask+0x8f8/0xa98)
[ 2452.810000] [<c013cef0>] (__alloc_pages_nodemask) from [<c013d2bc>] (alloc_kmem_pages+0x28/0xc0)
[ 2452.810000] [<c013d2bc>] (alloc_kmem_pages) from [<c01585d4>] (kmalloc_order+0x20/0x38)
[ 2452.810000] [<c01585d4>] (kmalloc_order) from [<c0158618>] (kmalloc_order_trace+0x2c/0x110)
[ 2452.810000] [<c0158618>] (kmalloc_order_trace) from [<c01783ac>] (__kmalloc+0x2f4/0x364)
[ 2452.810000] [<c01783ac>] (__kmalloc) from [<c052b868>] (ffs_epfile_io+0xb0/0x4a4)
[ 2452.810000] [<c052b868>] (ffs_epfile_io) from [<c052be44>] (ffs_epfile_read_iter+0xb4/0x170)
[ 2452.810000] [<c052be44>] (ffs_epfile_read_iter) from [<c018b7e4>] (__vfs_read+0xbc/0xe4)
[ 2452.810000] [<c018b7e4>] (__vfs_read) from [<c018bfbc>] (vfs_read+0x88/0x114)
[ 2452.810000] [<c018bfbc>] (vfs_read) from [<c018c8e4>] (SyS_read+0x4c/0xa0)
[ 2452.810000] [<c018c8e4>] (SyS_read) from [<c0010ef4>] (__sys_trace_return+0x0/0x10)
[ 2452.895000] Mem-Info:
[ 2452.895000] active_anon:22405 inactive_anon:183 isolated_anon:0
[ 2452.895000]  active_file:12599 inactive_file:42754 isolated_file:4
[ 2452.895000]  unevictable:3 dirty:29 writeback:0 unstable:0
[ 2452.895000]  slab_reclaimable:3331 slab_unreclaimable:4106
[ 2452.895000]  mapped:14507 shmem:325 pagetables:960 bounce:0
[ 2452.895000]  free:30893 free_pcp:21 free_cma:30150
[ 2452.930000] DMA free:124524kB min:2360kB low:2948kB high:3540kB active_anon:89620kB inactive_anon:732kB active_file:50376kB inactive_file:169800kB unevictable:12kB isolated(anon):0kB isolated(file):16kB present:507904kB managed:488348kB mlocked:12kB dirty:116kB writeback:0kB mapped:58028kB shmem:1300kB slab_reclaimable:13324kB slab_unreclaimable:16424kB kernel_stack:2648kB pagetables:3840kB unstable:0kB bounce:0kB free_pcp:452kB local_pcp:0kB free_cma:120600kB writeback_tmp:0kB pages_scanned:428 all_unreclaimable? no
[ 2452.975000] lowmem_reserve[]: 0 0 0 0
[ 2452.980000] DMA: 389*4kB (UMC) 125*8kB (MEC) 84*16kB (UMEC) 52*32kB (UMC) 34*64kB (UC) 35*128kB (UC) 30*256kB (UC) 28*512kB (C) 20*1024kB (C) 14*2048kB (C) 10*4096kB (C) = 124348kB
[ 2452.995000] 55510 total pagecache pages
[ 2453.000000] 126976 pages RAM
[ 2453.005000] 0 pages HighMem/MovableOnly
[ 2453.005000] 4889 pages reserved
[ 2453.010000] 32768 pages cma reserved

Change-Id: I3cef431057ac9e22483f4960bc3265132f6c4b41