On 2/27/12 3:09 AM, Zheng Liu wrote: > Hi list, > > Now, in ext4, we have multi-block allocation and delay allocation. They work > well for most scenarios. However, in some specific scenarios, they cannot help > us to optimize block allocation. For example, the user may want to indicate some > file set to be allocated at the beginning of the disk because its speed in this > position is faster than its speed at the end of disk. I agree with Lukas - please, no. You can play tricks with your storage to accomplish much the same thing, by making filesystems on faster & slower devices and mounting them on directories which your application can recognize as faster/slower. If you want "fast" for metadata, adilger has a recipe out there for using lvm to interleave ssd blocks with spinning blocks to get metadata to line up on the ssd. A filesystem-specific hack for a custom application has no place in EXT4, IMHO, sorry. Essentially this would move allocation decisions to userspace, and I don't think that sounds like a good idea. If nothing else, the application shouldn't assume that it "knows" anything at all about which regions of a filesystem may be faster or slower... -Eric > I have done the following experiment. The experiment is on my own server, which > has 16 Intel(R) Xeon(R) CPU E5620 @ 2.40GHz, 48G memory and a 1T sas disk. I > split this disk into two partitions, one has 900G, and another has 100G. Then I > use dd to get the speed of read/write. The result is as following. > > [READ] > # dd if=/dev/sdk1 of=/dev/null bs=128k count=10000 iflag=direct > 1310720000 bytes (1.3 GB) copied, 9.41151 s, 139 MB/s > > # dd if=/dev/sdk2 of=/dev/null bs=128k count=10000 iflag=direct > 1310720000 bytes (1.3 GB) copied, 17.952 s, 73.0 MB/s > > [WRITE] > # dd if=/dev/zero of=/dev/sdk1 bs=128k count=10000 oflag=direct > 1310720000 bytes (1.3 GB) copied, 8.46005 s, 155 MB/s > > # dd if=/dev/zero of=/dev/sdk2 bs=128k count=10000 oflag=direct > 1310720000 bytes (1.3 GB) copied, 15.8493 s, 82.7 MB/s > > So filesystem can provide a new feature to let the user to indicate a value > for reserving some blocks from the beginning of the disk. When the user needs > to allocate some blocks for an important file that needs to be read/write as > quick as possible, the user can use ioctl(2) and/or other ways to notify > filesystem to allocate these blocks in the reservation area. Thereby, the user > can obtain the higher performance for manipulating this file set. > > This idea is very trivial. So any comments or suggestions are appreciated. > > Regards, > Zheng > -- > 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 -- 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
