On 2017-08-03 13:44, Marat Khalili wrote: > On 02/08/17 20:52, Goffredo Baroncelli wrote: >> consider the following scenario: >> >> a) create a 2GB file >> b) fallocate -o 1GB -l 2GB >> c) write from 1GB to 3GB >> >> after b), the expectation is that c) always succeed [1]: i.e. there is enough space on the filesystem. Due to the COW nature of BTRFS, you cannot rely on the already allocated space because there could be a small time window where both the old and the new data exists on the disk. > Just curious. With current implementation, in the following case: > a) create a 2GB file1 && create a 2GB file2 > b) fallocate -o 1GB -l 2GB file1 && fallocate -o 1GB -l 2GB file2 A this step you are trying to allocate 3GB+3GB = 6GB, so you exhausted the filesystem space. > c) write from 1GB to 3GB file1 && write from 1GB to 3GB file2 > will (c) always succeed? I.e. does fallocate really allocate 2GB per file, or does it only allocate additional 1GB and check free space for another 1GB? If it's only the latter, it is useless. The file is physically extended ghigo@venice:/tmp$ fallocate -l 1000 foo.txt ghigo@venice:/tmp$ ls -l foo.txt -rw-r--r-- 1 ghigo ghigo 1000 Aug 3 18:00 foo.txt ghigo@venice:/tmp$ fallocate -o 500 -l 1000 foo.txt ghigo@venice:/tmp$ ls -l foo.txt -rw-r--r-- 1 ghigo ghigo 1500 Aug 3 18:00 foo.txt ghigo@venice:/tmp$ > > -- > > With Best Regards, > Marat Khalili > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
