On 2.03.2018 10:21, Misono, Tomohiro wrote: > On 2018/03/02 14:22, Qu Wenruo wrote: >> Btrfs shows max_inline option into kernel message, but for >> max_inline=4096, btrfs won't really inline 4096 bytes inline data if >> it's not compressed. > > Hello, > I have a question. > > man mount(8) says: > max_inline=bytes > Specify the maximum amount of space, in bytes, that can be > inlined in a metadata B-tree leaf. The value is specified in > bytes, optionally with a K, M, or G suffix, case insensitive. > In practice, this value is limited by the root sector size, > with some space unavailable due to leaf headers. For a 4k > sectorsize, max inline data is ~3900 bytes. > > So, is the size of 4k-(size of leaf header) actually the maximum value > of max_inline instead of 4095 for 4k sectorsize?
I think the documentation is wrong. Without patch 3/5 we have the max inline data size as: BTRFS_MAX_ITEM_SIZE(info) - BTRFS_FILE_EXTENT_INLINE_DATA_START so MAX_ITEM_SIZE = nodesize - sizeof(btrfs_header) - sizeof(btrfs_item). So this gives us the data portion in the leaf. So if we substitute the raw number we get: 16k - 101 - 25 = 16258 bytes. >From this number we also subtract the offset of disk_bytenr in btrfs_file_extent_item (which is 21). So we end up with MAX_INLINE_DATA_SIZE of 16258 - 21 = 16237 With Qu's patch the min_t will always be taking 4095 as the MAX_INLINE_DATA_SIZE. > > Thanks, > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
