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Date: Tue, 4 Apr 2017 11:17:06 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
kernel-team@....com
Subject: Re: [PATCH 2/5] zram: partial IO refactoring
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
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