On Sun, Sep 27, 2020 at 09:46:44AM +0300, Leon Romanovsky wrote: > +struct scatterlist *__sg_alloc_table_from_pages(struct sg_table *sgt, > + struct page **pages, unsigned int n_pages, unsigned int offset, > + unsigned long size, unsigned int max_segment, > + struct scatterlist *prv, unsigned int left_pages, > + gfp_t gfp_mask) > { > - unsigned int chunks, cur_page, seg_len, i; > + unsigned int chunks, cur_page, seg_len, i, prv_len = 0; > + struct scatterlist *s = prv; > + unsigned int table_size; > + unsigned int tmp_nents; > int ret; > - struct scatterlist *s; > > if (WARN_ON(!max_segment || offset_in_page(max_segment))) > - return -EINVAL; > + return ERR_PTR(-EINVAL); > + if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && prv) > + return ERR_PTR(-EOPNOTSUPP); > + > + tmp_nents = prv ? sgt->nents : 0; > + > + if (prv && > + page_to_pfn(sg_page(prv)) + (prv->length >> PAGE_SHIFT) ==
This calculation of the end doesn't consider sg->offset > + page_to_pfn(pages[0])) > + prv_len = prv->length; > > /* compute number of contiguous chunks */ > chunks = 1; > @@ -410,13 +461,17 @@ int __sg_alloc_table_from_pages(struct sg_table *sgt, > struct page **pages, > } > } > > - ret = sg_alloc_table(sgt, chunks, gfp_mask); > - if (unlikely(ret)) > - return ret; > + if (!prv) { > + /* Only the last allocation could be less than the maximum */ > + table_size = left_pages ? SG_MAX_SINGLE_ALLOC : chunks; > + ret = sg_alloc_table(sgt, table_size, gfp_mask); > + if (unlikely(ret)) > + return ERR_PTR(ret); > + } This is basically redundant right? Now that get_next_sg() can allocate SGs it can just build them one by one, no need to preallocate. Actually all the changes the the allocation seem like overkill, just allocate a single new array directly in get_next_sg() whenever it needs. Something like this: @@ -365,6 +372,37 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask) } EXPORT_SYMBOL(sg_alloc_table); +static struct scatterlist *get_next_sg(struct sg_table *table, + struct scatterlist *cur, unsigned long needed_sges, + gfp_t gfp_mask) +{ + struct scatterlist *new_sg; + unsigned int alloc_size; + + if (cur) { + struct scatterlist *next_sg = sg_next(cur); + + /* Check if last entry should be keeped for chainning */ + if (!sg_is_last(next_sg) || needed_sges == 1) + return next_sg; + } + + alloc_size = min_t(unsigned long, needed_sges, SG_MAX_SINGLE_ALLOC); + new_sg = sg_kmalloc(alloc_size, gfp_mask); + if (!new_sg) + return ERR_PTR(-ENOMEM); + sg_init_table(new_sg, alloc_size); + if (cur) { + __sg_chain(cur, new_sg); + table->orig_nents += alloc_size - 1; + } else { + table->sgl = new_sg; + table->orig_nents = alloc_size; + table->nents = 0; + } + return new_sg; +} + /** * __sg_alloc_table_from_pages - Allocate and initialize an sg table from * an array of pages @@ -374,29 +412,64 @@ EXPORT_SYMBOL(sg_alloc_table); * @offset: Offset from start of the first page to the start of a buffer * @size: Number of valid bytes in the buffer (after offset) * @max_segment: Maximum size of a scatterlist node in bytes (page aligned) + * @prv: Last populated sge in sgt + * @left_pages: Left pages caller have to set after this call * @gfp_mask: GFP allocation mask * - * Description: - * Allocate and initialize an sg table from a list of pages. Contiguous - * ranges of the pages are squashed into a single scatterlist node up to the - * maximum size specified in @max_segment. An user may provide an offset at a - * start and a size of valid data in a buffer specified by the page array. - * The returned sg table is released by sg_free_table. + * Description: + * If @prv is NULL, allocate and initialize an sg table from a list of pages, + * else reuse the scatterlist passed in at @prv. + * Contiguous ranges of the pages are squashed into a single scatterlist + * entry up to the maximum size specified in @max_segment. A user may + * provide an offset at a start and a size of valid data in a buffer + * specified by the page array. * * Returns: - * 0 on success, negative error on failure + * Last SGE in sgt on success, PTR_ERR on otherwise. + * The allocation in @sgt must be released by sg_free_table. + * + * Notes: + * If this function returns non-0 (eg failure), the caller must call + * sg_free_table() to cleanup any leftover allocations. */ -int __sg_alloc_table_from_pages(struct sg_table *sgt, struct page **pages, - unsigned int n_pages, unsigned int offset, - unsigned long size, unsigned int max_segment, - gfp_t gfp_mask) +struct scatterlist *__sg_alloc_table_from_pages(struct sg_table *sgt, + struct page **pages, unsigned int n_pages, unsigned int offset, + unsigned long size, unsigned int max_segment, + struct scatterlist *prv, unsigned int left_pages, + gfp_t gfp_mask) { - unsigned int chunks, cur_page, seg_len, i; - int ret; - struct scatterlist *s; + unsigned int chunks, cur_page, seg_len, i, prv_len = 0; + unsigned int added_nents = 0; + struct scatterlist *s = prv; if (WARN_ON(!max_segment || offset_in_page(max_segment))) - return -EINVAL; + return ERR_PTR(-EINVAL); + if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && prv) + return ERR_PTR(-EOPNOTSUPP); + + if (prv) { + unsigned long paddr = (page_to_pfn(sg_page(prv)) * PAGE_SIZE + + prv->offset + prv->length) / + PAGE_SIZE; + + if (WARN_ON(offset)) + return ERR_PTR(-EINVAL); + + /* Merge contiguous pages into the last SG */ + prv_len = prv->length; + while (n_pages && page_to_pfn(pages[0]) == paddr) { + if (prv->length + PAGE_SIZE > max_segment) + break; + prv->length += PAGE_SIZE; + paddr++; + pages++; + n_pages--; + } + if (!n_pages) { + sg_mark_end(sg_next(prv)); + return prv; + } + } /* compute number of contiguous chunks */ chunks = 1; @@ -410,13 +483,9 @@ int __sg_alloc_table_from_pages(struct sg_table *sgt, struct page **pages, } } - ret = sg_alloc_table(sgt, chunks, gfp_mask); - if (unlikely(ret)) - return ret; - /* merging chunks and putting them into the scatterlist */ cur_page = 0; - for_each_sg(sgt->sgl, s, sgt->orig_nents, i) { + for (i = 0; i < chunks; i++) { unsigned int j, chunk_size; /* look for the end of the current chunk */ @@ -429,15 +498,28 @@ int __sg_alloc_table_from_pages(struct sg_table *sgt, struct page **pages, break; } + /* Pass how many chunks might be left */ + s = get_next_sg(sgt, s, chunks - i + left_pages, gfp_mask); + if (IS_ERR(s)) { + /* + * Adjust entry length to be as before function was + * called. + */ + if (prv) + prv->length = prv_len; + return s; + } chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset; sg_set_page(s, pages[cur_page], min_t(unsigned long, size, chunk_size), offset); + added_nents++; size -= chunk_size; offset = 0; cur_page = j; } - - return 0; + sgt->nents += added_nents; + sg_mark_end(s); + return s; } EXPORT_SYMBOL(__sg_alloc_table_from_pages);