On Wed, Jan 09, 2008 at 05:06:33PM -0500, Rik van Riel wrote: ... > > > > Lather, rinse, repeat....
Just verified this at one customer site; they had a db that was last backed up in 2003 :/ > > On the other hand, updating the mtime and ctime whenever a page is dirtied > also does not work right. Apparently that can break mutt. > Thinking back on the atime discussion, I bet there would be some performance problems in updating the ctime/mtime that often too :) > Calling msync() every once in a while with Anton's patch does not look like a > fool proof method to me either, because the VM can write all the dirty pages > to disk by itself, leaving nothing for msync() to detect. (I think...) Reading the man page: "The st_ctime and st_mtime fields of a file that is mapped with MAP_SHARED and PROT_WRITE will be marked for update at some point in the interval between a write reference to the mapped region and the next call to msync() with MS_ASYNC or MS_SYNC for that portion of the file by any process. If there is no such call, these fields may be marked for update at any time after a write reference if the underlying file is modified as a result." So, whenever someone writes in the region, this must cause us to update the mtime/ctime no later than at the time of the next call to msync(). Could one do something like the lazy atime updates, coupled with a forced flush at msync()? > Can we get by with simply updating the ctime and mtime every time msync() > is called, regardless of whether or not the mmaped pages were still dirty > by the time we called msync() ? The update must still happen, eventually, after a write to the mapped region followed by an unmap/close even if no msync is ever called. The msync only serves as a "no later than" deadline. The write to the region triggers the need for the update. At least this is how I read the standard - please feel free to correct me if I am mistaken. -- / jakob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
