Hello, On (04/18/17 08:53), Minchan Kim wrote: > On Mon, Apr 17, 2017 at 07:50:16PM +0900, Sergey Senozhatsky wrote: > > 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. > > I can do but before that, I want to confirm. Ccing Matthew, > Summary for Matthew, > > I see following comment about the sector from bdev_read_page. > > /** > * 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 > * > > Does it mean that sector can be not aligned PAGE_SIZE? > > For example, 512byte sector, 4K page system, 4K = 8 sector > > bdev_read_page(bdev, 9, page); do you mean a sector that spans two pages? sectors are pow of 2 in size and pages are pow of 2 in size, so page_size is `K * sector_size', isn't it? fs/mpage.c static struct bio * do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages, sector_t *last_block_in_bio, struct buffer_head *map_bh, unsigned long *first_logical_block, get_block_t get_block, gfp_t gfp) { const unsigned blkbits = inode->i_blkbits; const unsigned blocks_per_page = PAGE_SIZE >> blkbits; const unsigned blocksize = 1 << blkbits; sector_t block_in_file; sector_t last_block; sector_t last_block_in_file; sector_t blocks[MAX_BUF_PER_PAGE]; ... block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits); last_block = block_in_file + nr_pages * blocks_per_page; last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits; if (last_block > last_block_in_file) last_block = last_block_in_file; or did I misunderstood your question? -ss