Commit 9ae77198 authored by Gao Xiang's avatar Gao Xiang
Browse files

erofs: tidy up z_erofs_lz4_handle_overlap() 



 - Add some useful comments to explain inplace I/Os and decompression;

 - Rearrange the code to get rid of one unnecessary goto.

Reviewed-by: default avatarChao Yu <chao@kernel.org>
Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
parent d53cd891

fs/erofs/decompressor.c

+46 −39
Original line number Diff line number Diff line
@@ -105,30 +105,20 @@ static int z_erofs_lz4_prepare_dstpages(struct z_erofs_decompress_req *rq, 
	return kaddr ? 1 : 0;

}



static void *z_erofs_lz4_handle_overlap(struct z_erofs_decompress_req *rq,

static void *z_erofs_lz4_handle_overlap(const struct z_erofs_decompress_req *rq,

			void *inpage, void *out, unsigned int *inputmargin,

			int *maptype, bool may_inplace)

{

	unsigned int oend, omargin, total, i;

	unsigned int oend, omargin, cnt, i;

	struct page **in;

	void *src, *tmp;



	if (rq->inplace_io) {

		oend = rq->pageofs_out + rq->outputsize;

		omargin = PAGE_ALIGN(oend) - oend;

		if (rq->partial_decoding || !may_inplace ||

		    omargin < LZ4_DECOMPRESS_INPLACE_MARGIN(rq->inputsize))

			goto docopy;



		for (i = 0; i < rq->inpages; ++i)

			if (rq->out[rq->outpages - rq->inpages + i] !=

			    rq->in[i])

				goto docopy;

		kunmap_local(inpage);

		*maptype = 3;

		return out + ((rq->outpages - rq->inpages) << PAGE_SHIFT);

	}

	void *src;



	/*

	 * If in-place I/O isn't used, for example, the bounce compressed cache

	 * can hold data for incomplete read requests. Just map the compressed

	 * buffer as well and decompress directly.

	 */

	if (!rq->inplace_io) {

		if (rq->inpages <= 1) {

			*maptype = 0;

			return inpage;
@@ -139,10 +129,34 @@ static void *z_erofs_lz4_handle_overlap(struct z_erofs_decompress_req *rq, 
			return ERR_PTR(-ENOMEM);

		*maptype = 1;

		return src;



docopy:

	/* Or copy compressed data which can be overlapped to per-CPU buffer */

	in = rq->in;

	}

	/*

	 * Then, deal with in-place I/Os. The reasons why in-place I/O is useful

	 * are: (1) It minimizes memory footprint during the I/O submission,

	 * which is useful for slow storage (including network devices and

	 * low-end HDDs/eMMCs) but with a lot inflight I/Os; (2) If in-place

	 * decompression can also be applied, it will reuse the unique buffer so

	 * that no extra CPU D-cache is polluted with temporary compressed data

	 * for extreme performance.

	 */

	oend = rq->pageofs_out + rq->outputsize;

	omargin = PAGE_ALIGN(oend) - oend;

	if (!rq->partial_decoding && may_inplace &&

	    omargin >= LZ4_DECOMPRESS_INPLACE_MARGIN(rq->inputsize)) {

		for (i = 0; i < rq->inpages; ++i)

			if (rq->out[rq->outpages - rq->inpages + i] !=

			    rq->in[i])

				break;

		if (i >= rq->inpages) {

			kunmap_local(inpage);

			*maptype = 3;

			return out + ((rq->outpages - rq->inpages) << PAGE_SHIFT);

		}

	}

	/*

	 * If in-place decompression can't be applied, copy compressed data that

	 * may potentially overlap during decompression to a per-CPU buffer.

	 */

	src = z_erofs_get_gbuf(rq->inpages);

	if (!src) {

		DBG_BUGON(1);
@@ -150,20 +164,13 @@ static void *z_erofs_lz4_handle_overlap(struct z_erofs_decompress_req *rq, 
		return ERR_PTR(-EFAULT);

	}



	tmp = src;

	total = rq->inputsize;

	while (total) {

		unsigned int page_copycnt =

			min_t(unsigned int, total, PAGE_SIZE - *inputmargin);



	for (i = 0, in = rq->in; i < rq->inputsize; i += cnt, ++in) {

		cnt = min_t(u32, rq->inputsize - i, PAGE_SIZE - *inputmargin);

		if (!inpage)

			inpage = kmap_local_page(*in);

		memcpy(tmp, inpage + *inputmargin, page_copycnt);

		memcpy(src + i, inpage + *inputmargin, cnt);

		kunmap_local(inpage);

		inpage = NULL;

		tmp += page_copycnt;

		total -= page_copycnt;

		++in;

		*inputmargin = 0;

	}

	*maptype = 2;