On Wed, Jul 21, 2021 at 08:43:00AM +0200, Andreas Grünbacher wrote: > Am Mi., 21. Juli 2021 um 04:54 Uhr schrieb Gao Xiang > <hsiangkao@xxxxxxxxxxxxxxxxx>: > > Hi Andreas, > > > > On Wed, Jul 21, 2021 at 04:26:47AM +0200, Andreas Grünbacher wrote: > > > Am Mi., 21. Juli 2021 um 02:33 Uhr schrieb Gao Xiang > > > <hsiangkao@xxxxxxxxxxxxxxxxx>: > > > > > And since you can only kmap one page at a time, an inline read grabs the > > > > > first part of the data in "page one" and then we have to call > > > > > iomap_begin a second time get a new address so that we can read the rest > > > > > from "page two"? > > > > > > > > Nope, currently EROFS inline data won't cross page like this. > > > > > > > > But in principle, yes, I don't want to limit it to the current > > > > EROFS or gfs2 usage. I think we could make this iomap function > > > > more generally (I mean, I'd like to make the INLINE extent > > > > functionity as general as possible, > > > > > > Nono. Can we please limit this patch what we actually need right now, > > > and worry about extending it later? > > > > Can you elaborate what it will benefit us if we only support one tail > > block for iomap_read_inline_data()? (I mean it has similar LOC changes, > > similar implementation / complexity.) The only concern I think is if > > it causes gfs2 regression, so that is what I'd like to confirm. > > iomap_read_inline_data supports one inline page now (i.e., from the > beginning of the file). It seems that you don't need more than one > tail page in EROFS, right? > > You were speculating about inline data in the middle of a file. That > sounds like a really, really bad idea to me, and I don't think we > should waste any time on it. Huh? why do you think it's a bad idea? I could give real example to you. At least, it can be used for some encoded data or repeated pattern (such as AABBAABBAABB...) in a packed way (marked in extent metadata). Is that enough? Again, I don't see what the benefits if limiting it to one tail block, it (maybe) just modifies: + /* handle tail-packing blocks cross the current page into the next */ + size = min_t(unsigned int, iomap->length + pos - iomap->offset, + PAGE_SIZE - poff); to + size = min_t(unsigned int, i_blocksize(inode), + PAGE_SIZE - poff); And which has the similar complexity, so why not using iomap->length here instead? Thanks, Gao Xiang
