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>> + struct page *start = NULL; >> + unsigned long start_sec; >> + unsigned long i; >> + bool can_free; >> + >> + /* >> + * Chunk the range into contiguous runs of pages for which the refcount >> + * went to zero and for which free_pages_prepare() succeeded. If >> + * free_pages_prepare() fails we consider the page to have been freed; >> + * deliberately leak it. >> + * >> + * Code assumes contiguous PFNs have contiguous struct pages, but not >> + * vice versa. Break batches at section boundaries since pages from >> + * different sections must not be coalesced into a single high-order >> + * block. > > The comment is not completely accurate: section boundary only applies to > some kernel configs. > > Maybe rewrite the whole paragraph into > > "Contiguous PFNs might not have a contiguous "struct pages" in some > kernel config. Therefore, check memdesc_section(), and stop batching > once it changes, see num_pages_contiguous()." Agreed, I'll update. > >> + */ >> + for (i = 0; i < nr_pages; i++, page++) { >> + VM_WARN_ON_ONCE(PageHead(page)); >> + VM_WARN_ON_ONCE(PageTail(page)); >> + >> + can_free = put_page_testzero(page); >> + if (can_free && !free_pages_prepare(page, 0)) >> + can_free = false; >> + >> + if (can_free && start && >> + memdesc_section(page->flags) != start_sec) { >> + free_prepared_contig_range(start, page - start); >> + start = page; >> + start_sec = memdesc_section(page->flags); >> + } else if (!can_free && start) { >> + free_prepared_contig_range(start, page - start); >> + start = NULL; >> + } else if (can_free && !start) { >> + start = page; >> + start_sec = memdesc_section(page->flags); >> + } >> + } > > Simplification a proposed by Zi make sense to me! I've added it. Thanks, Usama