Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbdDDCRJ (ORCPT ); Mon, 3 Apr 2017 22:17:09 -0400 Received: from mail-pg0-f41.google.com ([74.125.83.41]:36575 "EHLO mail-pg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752219AbdDDCRH (ORCPT ); Mon, 3 Apr 2017 22:17:07 -0400 Date: Tue, 4 Apr 2017 11:17:06 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, Sergey Senozhatsky , kernel-team@lge.com Subject: Re: [PATCH 2/5] zram: partial IO refactoring Message-ID: <20170404021706.GA475@jagdpanzerIV.localdomain> References: <1491196653-7388-1-git-send-email-minchan@kernel.org> <1491196653-7388-3-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1491196653-7388-3-git-send-email-minchan@kernel.org> User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6300 Lines: 210 Hello, On (04/03/17 14:17), Minchan Kim wrote: > +static bool zram_special_page_read(struct zram *zram, u32 index, > + struct page *page, > + unsigned int offset, unsigned int len) > +{ > + struct zram_meta *meta = zram->meta; > + > + bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > + if (unlikely(!meta->table[index].handle) || > + zram_test_flag(meta, index, ZRAM_SAME)) { > + void *mem; > + > + bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > + mem = kmap_atomic(page); > + zram_fill_page(mem + offset, len, meta->table[index].element); > + kunmap_atomic(mem); > + return true; > + } > + bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > + > + return false; > +} > + > +static bool zram_special_page_write(struct zram *zram, u32 index, > + struct page *page) > +{ > + unsigned long element; > + void *mem = kmap_atomic(page); > + > + if (page_same_filled(mem, &element)) { > + struct zram_meta *meta = zram->meta; > + > + kunmap_atomic(mem); > + /* Free memory associated with this sector now. */ > + bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > + zram_free_page(zram, index); > + zram_set_flag(meta, index, ZRAM_SAME); > + zram_set_element(meta, index, element); > + bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > + > + atomic64_inc(&zram->stats.same_pages); > + return true; > + } > + kunmap_atomic(mem); > + > + return false; > +} zram_special_page_read() and zram_special_page_write() have a slightly different locking semantics. zram_special_page_read() copy-out ZRAM_SAME page having slot unlocked (can the slot got overwritten in the meantime?), while zram_special_page_write() keeps the slot locked through out the entire operation. > static void zram_meta_free(struct zram_meta *meta, u64 disksize) > { > size_t num_pages = disksize >> PAGE_SHIFT; > @@ -504,169 +548,104 @@ static void zram_free_page(struct zram *zram, size_t index) > zram_set_obj_size(meta, index, 0); > } > > -static int zram_decompress_page(struct zram *zram, char *mem, u32 index) > +static int zram_decompress_page(struct zram *zram, struct page *page, u32 index) > { > - int ret = 0; > - unsigned char *cmem; > - struct zram_meta *meta = zram->meta; > + int ret; > unsigned long handle; > unsigned int size; > + void *src, *dst; > + struct zram_meta *meta = zram->meta; > + > + if (zram_special_page_read(zram, index, page, 0, PAGE_SIZE)) > + return 0; > > bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > handle = meta->table[index].handle; > size = zram_get_obj_size(meta, index); > > - if (!handle || zram_test_flag(meta, index, ZRAM_SAME)) { > - bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > - zram_fill_page(mem, PAGE_SIZE, meta->table[index].element); > - return 0; > - } > - > - cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO); > + src = zs_map_object(meta->mem_pool, handle, ZS_MM_RO); > if (size == PAGE_SIZE) { > - copy_page(mem, cmem); > + dst = kmap_atomic(page); > + copy_page(dst, src); > + kunmap_atomic(dst); > + ret = 0; > } else { > struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp); > > - ret = zcomp_decompress(zstrm, cmem, size, mem); > + dst = kmap_atomic(page); > + ret = zcomp_decompress(zstrm, src, size, dst); > + kunmap_atomic(dst); > zcomp_stream_put(zram->comp); > } > zs_unmap_object(meta->mem_pool, handle); > bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > > /* Should NEVER happen. Return bio error if it does. */ > - if (unlikely(ret)) { > + if (unlikely(ret)) > pr_err("Decompression failed! err=%d, page=%u\n", ret, index); > - return ret; > - } > > - return 0; > + return ret; > } > > static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec, > - u32 index, int offset) > + u32 index, int offset) > { > int ret; > struct page *page; > - unsigned char *user_mem, *uncmem = NULL; > - struct zram_meta *meta = zram->meta; > - page = bvec->bv_page; > > - bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > - if (unlikely(!meta->table[index].handle) || > - zram_test_flag(meta, index, ZRAM_SAME)) { > - bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > - handle_same_page(bvec, meta->table[index].element); > + page = bvec->bv_page; > + if (zram_special_page_read(zram, index, page, bvec->bv_offset, > + bvec->bv_len)) so, I think zram_bvec_read() path calls zram_special_page_read() twice: a) direct zram_special_page_read() call b) zram_decompress_page()->zram_special_page_read() is it supposed to be so? > return 0; > - } > - bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > - > - if (is_partial_io(bvec)) > - /* Use a temporary buffer to decompress the page */ > - uncmem = kmalloc(PAGE_SIZE, GFP_NOIO); > - > - user_mem = kmap_atomic(page); > - if (!is_partial_io(bvec)) > - uncmem = user_mem; > > - if (!uncmem) { > - pr_err("Unable to allocate temp memory\n"); > - ret = -ENOMEM; > - goto out_cleanup; > + if (is_partial_io(bvec)) { > + /* Use a temporary buffer to decompress the page */ > + page = alloc_page(GFP_NOIO|__GFP_HIGHMEM); > + if (!page) > + return -ENOMEM; > } > > - ret = zram_decompress_page(zram, uncmem, index); > - /* Should NEVER happen. Return bio error if it does. */ > + ret = zram_decompress_page(zram, page, index); > if (unlikely(ret)) > - goto out_cleanup; > + goto out; > > - if (is_partial_io(bvec)) > - memcpy(user_mem + bvec->bv_offset, uncmem + offset, > - bvec->bv_len); > + if (is_partial_io(bvec)) { > + void *dst = kmap_atomic(bvec->bv_page); > + void *src = kmap_atomic(page); > > - flush_dcache_page(page); > - ret = 0; > -out_cleanup: > - kunmap_atomic(user_mem); > + memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len); > + kunmap_atomic(src); > + kunmap_atomic(dst); > + } > +out: > if (is_partial_io(bvec)) > - kfree(uncmem); > + __free_page(page); > + > return ret; > } > > -static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, > - int offset) > +static int zram_compress(struct zram *zram, struct zcomp_strm **zstrm, > + struct page *page, > + unsigned long *out_handle, unsigned int *out_comp_len) ok, I see why... not super happy with the `zstrm' magic, but OK. can do. -ss