> -----Original Message----- > From: Jaegeuk Kim [mailto:jaeg...@kernel.org] > Sent: Tuesday, January 05, 2016 11:30 AM > To: Chao Yu > Cc: 'Fan Li'; linux-f2fs-devel@lists.sourceforge.net > Subject: Re: [f2fs-dev] [PATCH 2/3] f2fs: support finding extents after isize > > 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? > > > > AFAIK, no more. > > > > > > > > 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. > > > > Append write in such inode could destroy this convention, right? > > Right, but we have another chance to reset the flag, when fiemap checks the > end > of allocated space.
Agreed, :) Thanks, > > Thanks, > > > > > Thanks, > > > > > > > > Thanks, > > > > > > > > > > > I think we can all agree both ideas have their flaws. > > > > The only divergence is that I vote the first, and you the second. I > > > > think the most important > > > thing is that it works fluently in most > > > > scenarios, and you think is that it works in every scenarios even it's > > > > very slow. > > > > > > > > I think my method is more pratical, but balance between performance and > > > > utility seems > to be > > > an Eternal problem. > > > > > > > > > > > > > > > > > > > > > use max blocks as boundary would get us the precise result, but it > > > > > > also means after we reach the EOF, we still need to look up every > > > > > > block between the EOF and sb-> s_maxbytes to make sure the EOF is > > > > > > true, that's about 4TB or 10^9 blocks. > > > > > > And it affects all scenarios where the search range covers the last > > > > > > extent in the file, not just extents beyond isize. I think this > > > > > > price > > > > > > is too high to pay. > > > > > > > > > > That's another performance issue. > > > > > > > > > > > > > > > > > I was hoping that I can make f2fs_map_block return an EOF to solve > > > > > > this problem some time later, or anyone have a better idea? > > > > > > > > > > At least we can seek valid dnode block like the way llseek use. > > > > > > > > > > In addition, for most cases, few of i_nid[5] in f2fs_inode will be > > > > > NULL, we could skip > searching > > > all dnode block in such > > > > non-allocated > > > > > indirect node, instead of searching dnode block f2fs_map_block one by > > > > > one. > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Fan li <fanofcode...@samsung.com> > > > > > > > > --- > > > > > > > > fs/f2fs/data.c | 7 +------ > > > > > > > > 1 file changed, 1 insertion(+), 6 deletions(-) > > > > > > > > > > > > > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index > > > > > > > > a9a4d89..f89cf07 > > > > > > > > 100644 > > > > > > > > --- a/fs/f2fs/data.c > > > > > > > > +++ b/fs/f2fs/data.c > > > > > > > > @@ -798,12 +798,6 @@ int f2fs_fiemap(struct inode *inode, > > > > > > > > struct fiemap_extent_info > > > *fieinfo, > > > > > > > > isize = i_size_read(inode); > > > > > > > > > > > > > > > > mutex_lock(&inode->i_mutex); > > > > > > > > - if (start >= isize) > > > > > > > > - goto out; > > > > > > > > - > > > > > > > > - if (start + len > isize) > > > > > > > > - len = isize - start; > > > > > > > > - > > > > > > > > if (logical_to_blk(inode, len) == 0) > > > > > > > > len = blk_to_logical(inode, 1); > > > > > > > > > > > > > > > > @@ -829,6 +823,7 @@ next: > > > > > > > > * punch holes beyond isize and keep size > > > > > > > > unchanged. > > > > > > > > */ > > > > > > > > flags |= FIEMAP_EXTENT_LAST; > > > > > > > > + last_blk = start_blk - 1; > > > > > > > > } > > > > > > > > > > > > > > > > if (size) > > > > > > > > > > > > > > > > > > > > > > > > > > ---------------------------------------------------------------------- > > > > > > -------- _______________________________________________ > > > > > > Linux-f2fs-devel mailing list > > > > > > Linux-f2fs-devel@lists.sourceforge.net > > > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel ------------------------------------------------------------------------------ _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
