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 majord...@vger.kernel.org > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
