On Mar 18, 2013, Chris Mason <chris.ma...@fusionio.com> wrote: > A few questions. Does leveldb use O_DIRECT and mmap together?
No, it doesn't use O_DIRECT at all. Its I/O interface is very simplified: it just opens each new file (database chunks limited to 2MB) with O_CREAT|O_RDWR|O_TRUNC, and then uses ftruncate, mmap, msync, munmap and fdatasync. It doesn't seem to modify data once it's written; it only appends. Reading data back from it uses a completely different class interface, using separate descriptors and using pread only. > (the source of a write being pages that are mmap'd from somewhere > else) AFAICT the source of the memcpy()s that append to the file are malloc()ed memory. > That's the most likely place for this kind of problem. Also, you > mention crc errors. Are those reported by btrfs or are they application > level crcs. These are CRCs leveldb computes and writes out after each db block. No btrfs CRC errors are reported in this process. -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer -- 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
