Hello Minchan, On (04/17/17 11:14), Minchan Kim wrote: > On Mon, Apr 17, 2017 at 10:54:29AM +0900, Sergey Senozhatsky wrote: > > On (04/17/17 10:21), Sergey Senozhatsky wrote: > > > > However, it should be *fixed* to prevent confusion in future > > > > or may be something like below? can save us some cycles. > > > > remove this calculation > > > > - offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; > > > > > > and pass 0 to zram_bvec_rw() > > > > - err = zram_bvec_rw(zram, &bv, index, offset, is_write); > > + err = zram_bvec_rw(zram, &bv, index, 0, is_write); > > That was one I wrote but have thought it more. > > Because I suspect fs can submit page-size IO in non-aligned PAGE_SIZE > sector? For example, it can submit PAGE_SIZE read request from 9 sector. > Is it possible? I don't know. > > As well, FS can format zram from sector 1, not sector 0? IOW, can't it > use starting sector as non-page algined sector? > We can do it via fdisk? > > Anyway, If one of scenario I mentioned is possible, zram_rw_page will > be broken. > > If it's hard to check all of scenario in this moment, it would be > better to not remove it and then add WARN_ON(offset) in there. > > While I am writing this, I found this. > > /** > * bdev_read_page() - Start reading a page from a block device > * @bdev: The device to read the page from > * @sector: The offset on the device to read the page to (need not be aligned) > * @page: The page to read > * > > Hmm,, need investigation but no time. good questions. as far as I can see, we never use 'offset' which we pass to zram_bvec_rw() from zram_rw_page(). `offset' makes a lot of sense for partial IO, but in zram_bvec_rw() we always do "bv.bv_len = PAGE_SIZE". so what we have is for READ zram_rw_page() bv.bv_len = PAGE_SIZE zram_bvec_rw(zram, &bv, index, offset, is_write); zram_bvec_read() if (is_partial_io(bvec)) // always false memcpy(user_mem + bvec->bv_offset, uncmem + offset, bvec->bv_len); for WRITE zram_rw_page() bv.bv_len = PAGE_SIZE zram_bvec_rw(zram, &bv, index, offset, is_write); zram_bvec_write() if (is_partial_io(bvec)) // always false memcpy(uncmem + offset, user_mem + bvec->bv_offset, bvec->bv_len); and our is_partial_io() looks at ->bv_len: bvec->bv_len != PAGE_SIZE; which we set to PAGE_SIZE. so in the existing scheme of things, we never care about 'sector' passed from zram_rw_page(). and this has worked for us for quite some time. my call would be -- let's drop zram_rw_page() `sector' calculation. -ss