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SubjectRe: [PATCH] erofs: remove the fast path of per-CPU buffer decompression
On Thu, Oct 14, 2021 at 01:57:56PM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2@yulong.com>
>
> As Xiang mentioned, such path has no real impact to our current
> decompression strategy, remove it directly. Also, update the return
> value of z_erofs_lz4_decompress() to 0 if success to keep consistent
> with LZMA which will return 0 as well for that case.
>
> Signed-off-by: Yue Hu <huyue2@yulong.com>
> ---
> fs/erofs/decompressor.c | 64 +++++++------------------------------------------
> 1 file changed, 8 insertions(+), 56 deletions(-)
>
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index a5bc4b1..9905551 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -254,7 +254,7 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
> DBG_BUGON(1);
> return -EFAULT;
> }
> - return ret;
> + return ret > 0 ? 0 : ret;

How about just updating the else branch of "if (ret != rq->outputsize)"?

> }
>
> static struct z_erofs_decompressor decompressors[] = {
> @@ -268,33 +268,6 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
> },
> };
>
> -static void copy_from_pcpubuf(struct page **out, const char *dst,
> - unsigned short pageofs_out,
> - unsigned int outputsize)
> -{
> - const char *end = dst + outputsize;
> - const unsigned int righthalf = PAGE_SIZE - pageofs_out;
> - const char *cur = dst - pageofs_out;
> -
> - while (cur < end) {
> - struct page *const page = *out++;
> -
> - if (page) {
> - char *buf = kmap_atomic(page);
> -
> - if (cur >= dst) {
> - memcpy(buf, cur, min_t(uint, PAGE_SIZE,
> - end - cur));
> - } else {
> - memcpy(buf + pageofs_out, cur + pageofs_out,
> - min_t(uint, righthalf, end - cur));
> - }
> - kunmap_atomic(buf);
> - }
> - cur += PAGE_SIZE;
> - }
> -}
> -
> static int z_erofs_decompress_generic(struct z_erofs_decompress_req *rq,
> struct list_head *pagepool)
> {
> @@ -305,34 +278,13 @@ static int z_erofs_decompress_generic(struct z_erofs_decompress_req *rq,
> void *dst;
> int ret;
>
> - /* two optimized fast paths only for non bigpcluster cases yet */
> - if (rq->inputsize <= PAGE_SIZE) {
> - if (nrpages_out == 1 && !rq->inplace_io) {
> - DBG_BUGON(!*rq->out);
> - dst = kmap_atomic(*rq->out);
> - dst_maptype = 0;
> - goto dstmap_out;
> - }
> -
> - /*
> - * For the case of small output size (especially much less
> - * than PAGE_SIZE), memcpy the decompressed data rather than
> - * compressed data is preferred.
> - */
> - if (rq->outputsize <= PAGE_SIZE * 7 / 8) {
> - dst = erofs_get_pcpubuf(1);
> - if (IS_ERR(dst))
> - return PTR_ERR(dst);
> -
> - rq->inplace_io = false;
> - ret = alg->decompress(rq, dst);
> - if (!ret)
> - copy_from_pcpubuf(rq->out, dst, rq->pageofs_out,
> - rq->outputsize);
> -
> - erofs_put_pcpubuf(dst);
> - return ret;
> - }
> + /* one optimized fast path only for non bigpcluster cases yet */
> + if (rq->inputsize <= PAGE_SIZE &&
> + nrpages_out == 1 && !rq->inplace_io) {

How about rearrange these into one line? (it seems just 80 char).

Otherwise looks good to me.

Thanks,
Gao Xiang

> + DBG_BUGON(!*rq->out);
> + dst = kmap_atomic(*rq->out);
> + dst_maptype = 0;
> + goto dstmap_out;
> }
>
> /* general decoding path which can be used for all cases */
> --
> 1.9.1

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