On Tue, Feb 14, 2012 at 7:19 PM, Robin Dong <hao.bigrat@xxxxxxxxx> wrote: > But I found the code in ext4_ext_map_blocks(): > > if ((sbi->s_cluster_ratio > 1) && > ext4_find_delalloc_cluster(inode, map->m_lblk, 0)) > map->m_flags |= EXT4_MAP_FROM_CLUSTER; > > thus, even the delayed allocated block in the page-cache (have not be > allocated) already have been checked. Therefore in my opinion, the > EXT4_MAP_FROM_CLUSTER is a sufficient check. > > Follow the case of your long comment :) , process will go like this > in MY CODE ABOVE : > > [0-3], [4-7], [8-11] > > 1. delay-allocation write blocks 10&11 > we reserve 1 cluster, the i_reserved_data_blocks is 1 now > 2. delay-allocation write blocks 3 to 8 > we reserve other 2 clusters, so 3 clusters totally, the > i_reserved_data_blocks is 3 now > 3. writeout the blocks 3 to 8 > claim all 3 clusters, i_reserved_data_blocks is 0 now > At this moment, we really have allocated 3 clusters, and the > remain 10&11 block would never occupy another cluster (it would > definitely go into the [8-11] cluster), so, why need we reserve one > more cluster quota ? > 4. writeout the 10&11 blocks > the 10&11 blocks will be set EXT4_MAP_FROM_CLUSTER flag ( by > get_implied_cluster_alloc as the 8~9 block have been allocated), and > it will not call ext4_da_update_reserve_space any more > > As this, no warning, no reserve-and-release ping pong....at least in my imaging > I couldn't look into this in detail, but your logic seems totally fine. But when I wrote this code, I remember being able to reproduce the quota warnings by running xfstests (some corner case that needed this code). > Could you please point out what I missed ? > > Thanks > -- Aditya -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
