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SubjectRe: [PATCH] erofs: remove the fast path of per-CPU buffer decompression
On Thu, 14 Oct 2021 14:16:48 +0800
Gao Xiang <hsiangkao@linux.alibaba.com> wrote:

> 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)"?

Agree.

>
> > }
> >
> > 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).

aha, seems it's.

v2 will fix them.

Thanks.

>
> 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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