On Wed, Mar 30, 2016 at 02:58:38PM -0400, Austin S. Hemmelgarn wrote: > Nothing that I can find in the man-pages or API documentation for Linux's > fallocate explicitly says that it will be fast. There are bits that say it > should be efficient, but that is not itself well defined (given context, I > would assume it to mean that it doesn't use as much I/O as writing out that > many bytes of zero data, not necessarily that it will return quickly). And that's pretty much as narrow as an defintion we get. But apparently gfs2 already breaks that expectation :( > >delalloc system is careful enough to check that there are enough free > >blocks to handle both the allocation and the metadata updates. The > >only gap in this scheme that I can see is if we fallocate, crash, and > >upon restart the program then tries to write without retrying the > >fallocate. Can we trade some performance for the added requirement > >that we must fallocate -> write -> fsync, and retry the trio if we > >crash before the fsync returns? I think that's already an implicit > >requirement, so we might be ok here. > Most of the software I've seen that doesn't use fallocate like this is > either doing odd things otherwise, or is just making sure it has space for > temporary files, so I think it is probably safe to require this. posix_fallocate gurantees you that you don't get ENOSPC from the write, and there is plenty of software relying on that or crashing / cause data integrity problems that way. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
