Hi, ...
> > > > > > > > Nope, what I'm talking about is *correctness* of our > > > > > > > > ->fiemap interface, but you're trying to avoid it by saying > > > > > > > > "support more > > > > > > > cases, > > > > > > > > it's an improvement". That doesn't make any sense to me, since > > > > > > > > correctness issue still not be fixed. > > > > > > > > > > > > > > I'm not sure what you mean by avoiding, I think the comment > > > > > > > and reply I written has already stated the issue and limitation > > > > > > > of this patch. > > > > > > > Now there are two suggestions: > > > > > > > 1. support one more scenario, and all old scenarios are dealt > > > > > > > like before, but it still can't support discontinuous extent > > > > > > > after isize. > > > > > > > 2. support all scenarios, but sacrifice performance for lots of > > > > > > > common scenarios by checking about 10^9 blocks. > > > > > > > > > > > > IMO, we can think about #2 whether there is an efficient way. > > > > > > > > > > > > How many cases does this incur? > > > > > > One is fallocate with keeping i_size, ana other? > > > > > > > > > > > > How about adding FADVISE_OVER_ISIZE to represent inode has blocks > > > > > > beyond i_size? > > > > > > Then, we can set this flag in fallocate and reset it in > > > > > > f2fs_truncate. > > > > > > > > > > I have a similar idea that add an actual size which marks the end > > > > > of last extent, so we can know if the current extent is the last one, > > > > > even without searching for extents behind. > > > > > > > > Where do you want to store that size in disk? > > > > > > I'm still not very confident about this idea, so I didn't really think > > > that through yet, inode may be a proper place. > > > Or we just write a special function to find it, and call it only when > > > fiemap is called and disk size isn't initiated yet. After all this isn't > > > frequently-used. > > > > > > > > > > > > But there is a problem I still can't figure out, after truncate > > > > > an extent at the end of file beyond isize , how do I know where > > > > > the new last extent ends or if there are still extents beyond isize? > > > > > after all, the extents beyond isize could be > discontinuous. > > > > > > > > So, that's why I proposed a flag instead of a kind of i_disksize. > > > > We can just set the flag, only if a file *may* have a extent beyond > > > > i_size in fallocate, and unset it through f2fs_truncate. > > > > Moreover, I don't expect that this happens so frequently. > > > > > > if flag could indicate "may", will i_disksize do a better job in the same > > > way? > > > let i_disksize be the end of the last extent that *may* exist beyond > > > i_size, set it also in fallocate,when truncate, if the length is still > > > beyond isize, we set the new length as i_disksize, so in worse scenario > > > we won't have to search up to s_maxbytes. > > > > My real concern is that there no space for i_disksize. > > I see. How about combine both ideas, use flag as you propose, and if fiemap > ever needs to > look up the last extent beyond isize, we calculate i_disksize first and cache > it in f2fs_inode_info, > use it to determine the last extent. > > This way we don't have to look up all blocks up to s_maxbytes, and need no > extra space in disk. Looks good to me. Thanks, ------------------------------------------------------------------------------ _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
