On Fri, 12 Mar 2010, Raphael Hertzog wrote: > Other possibility would be to use the loop afterwards to reopen all > installed files and call fsync() on them. The disadvantage of sync() is > obviously when unrelated disk activity happens in parallel to dpkg, it > will have to wait more due to this.
My guess is that doing fsync in a loop afterwards will have the same impact as doing fsync during the unpack phase. I think the main problem here is that of I/O reordering not happening when you do fsync, and if the files are not ordered in an advantageous way on the disk compared to the order they are unpacked, the resulting seeks can have a disastrous impact on performance. So, IMHO, what you really want to do is unpack, sync everything, and then rename. Unfortunately, there exists nothing that permits to sync only a set of files, and as was said in this thread, sync() doesn't necessarily guarantees all writes happened once it returns, though that might be true on Linux. One could think of using FIEMAP to reorder the fsyncs, but there are chances that this wouldn't work on ext4 and other fs that use delayed allocation, in which case you'll probably only get FIEMAP_EXTENT_UNKNOWN. Mike PS: I'm not subscribed, please Cc me. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/[email protected]
