On (24/03/28 10:48), Barry Song wrote:
[..]
> +/*
> + * Use a temporary buffer to decompress the page, as the decompressor
> + * always expects a full page for the output.
> + */
> +static int zram_bvec_read_multi_pages_partial(struct zram *zram, struct bio_vec *bvec,
> + u32 index, int offset)
> +{
> + struct page *page = alloc_pages(GFP_NOIO | __GFP_COMP, ZCOMP_MULTI_PAGES_ORDER);
> + int ret;
> +
> + if (!page)
> + return -ENOMEM;
> + ret = zram_read_multi_pages(zram, page, index, NULL);
> + if (likely(!ret)) {
> + atomic64_inc(&zram->stats.zram_bio_read_multi_pages_partial_count);
> + void *dst = kmap_local_page(bvec->bv_page);
> + void *src = kmap_local_page(page);
> +
> + memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len);
> + kunmap_local(src);
> + kunmap_local(dst);
> + }
> + __free_pages(page, ZCOMP_MULTI_PAGES_ORDER);
> + return ret;
> +}
[..]
> +static int zram_bvec_write_multi_pages_partial(struct zram *zram, struct bio_vec *bvec,
> + u32 index, int offset, struct bio *bio)
> +{
> + struct page *page = alloc_pages(GFP_NOIO | __GFP_COMP, ZCOMP_MULTI_PAGES_ORDER);
> + int ret;
> + void *src, *dst;
> +
> + if (!page)
> + return -ENOMEM;
> +
> + ret = zram_read_multi_pages(zram, page, index, bio);
> + if (!ret) {
> + src = kmap_local_page(bvec->bv_page);
> + dst = kmap_local_page(page);
> + memcpy(dst + offset, src + bvec->bv_offset, bvec->bv_len);
> + kunmap_local(dst);
> + kunmap_local(src);
> +
> + atomic64_inc(&zram->stats.zram_bio_write_multi_pages_partial_count);
> + ret = zram_write_page(zram, page, index);
> + }
> + __free_pages(page, ZCOMP_MULTI_PAGES_ORDER);
> + return ret;
> +}
What type of testing you run on it? How often do you see partial
reads and writes? Because this looks concerning - zsmalloc memory
usage reduction is one metrics, but this also can be achieved via
recompression, writeback, or even a different compression algorithm,
but higher CPU/power usage/higher requirements for physically contig
pages cannot be offset easily. (Another corner case, assume we have
partial read requests on every CPU simultaneously.)
