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Tue, 30 Jun 2026 06:54:26 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 30 Jun 2026 15:54:24 +0200 To: Wen Jiang Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, urezki@gmail.com, baohua@kernel.org, Xueyuan.chen21@gmail.com, dev.jain@arm.com, rppt@kernel.org, david@kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, ajd@linux.ibm.com, linux-kernel@vger.kernel.org, jiangwen6@xiaomi.com, shanghaoqiang@xiaomi.com Subject: Re: [PATCH v4 5/6] mm/vmalloc: map contiguous pages in batches for vmap() if possible Message-ID: References: <20260618084726.1070022-1-jiangwen6@xiaomi.com> <20260618084726.1070022-6-jiangwen6@xiaomi.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260618084726.1070022-6-jiangwen6@xiaomi.com> On Thu, Jun 18, 2026 at 04:47:25PM +0800, Wen Jiang wrote: > From: "Barry Song (Xiaomi)" > > In many cases, the pages passed to vmap() may include high-order > pages. For example, the systemheap often allocates pages in descending > order: order 8, then 4, then 0. Currently, vmap() iterates over every > page individually—even pages inside a high-order block are handled > one by one. > > This patch detects physically contiguous pages (regardless of whether > they are compound or non-compound) by scanning with > num_pages_contiguous(), and maps them as a single contiguous block > whenever possible. The mapping order is determined by taking the > minimum of the contiguous page count and the pfn alignment, allowing > graceful degradation when pfn alignment is less than the contiguous > range. > > Pages with the same page_shift are coalesced and mapped via > vmap_pages_range_noflush_walk() to avoid page table rewalk. > > As users typically allocate memory in descending orders (e.g. > 8 → 4 → 0), once an order-0 page is encountered, we stop scanning > for contiguous pages since subsequent pages are likely order-0 as well. > > Signed-off-by: Barry Song (Xiaomi) > Co-developed-by: Dev Jain > Signed-off-by: Dev Jain > Signed-off-by: Wen Jiang > Tested-by: Xueyuan Chen > --- > mm/vmalloc.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 85 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 253e017130e09..fffb885cb2158 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3545,6 +3545,89 @@ void vunmap(const void *addr) > } > EXPORT_SYMBOL(vunmap); > > +static inline unsigned int vm_shift(pgprot_t prot, unsigned long size) > +{ > + if (arch_vmap_pmd_supported(prot) && size >= PMD_SIZE) > + return PMD_SHIFT; > + > + return arch_vmap_pte_supported_shift(size); > +} > + > +static inline int get_vmap_batch_order(struct page **pages, > + pgprot_t prot, unsigned int max_steps, unsigned int idx) > +{ > + unsigned int nr_contig; > + int order; > + > + if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMAP)) > + return 0; > + > + nr_contig = num_pages_contiguous(&pages[idx], max_steps); > + if (nr_contig < 2) > + return 0; > + > + order = ilog2(nr_contig); > + > + /* Limit order by pfn alignment */ > + order = min_t(int, order, __ffs(page_to_pfn(pages[idx]))); > + > + if (vm_shift(prot, PAGE_SIZE << order) == PAGE_SHIFT) > + return 0; > + > + return order; > +} > + > +static int vmap_batched(unsigned long addr, unsigned long end, > + pgprot_t prot, struct page **pages) > +{ > + unsigned int count = (end - addr) >> PAGE_SHIFT; > + unsigned int prev_shift = 0, idx = 0; > + unsigned long start = addr, map_addr = addr; > + int err; > + > + err = kmsan_vmap_pages_range_noflush(addr, end, prot, pages, > + PAGE_SHIFT, GFP_KERNEL); > + if (err) > + goto out; > + > + for (unsigned int i = 0; i < count; ) { > + unsigned int shift = PAGE_SHIFT + > + get_vmap_batch_order(pages, prot, count - i, i); > + > + if (!i) > + prev_shift = shift; > + > + if (shift != prev_shift) { > + err = vmap_pages_range_noflush_walk(map_addr, addr, > + prot, pages + idx, prev_shift); > + if (err) > + goto out; > + prev_shift = shift; > + map_addr = addr; > + idx = i; > + } > + > + /* > + * Once small pages are encountered, the remaining pages > + * are likely small as well. > + */ > + if (shift == PAGE_SHIFT) > + break; > + > + addr += 1UL << shift; > + i += 1U << (shift - PAGE_SHIFT); > + } > + > + /* Remaining */ > + if (map_addr < end) > + err = vmap_pages_range_noflush_walk(map_addr, end, > + prot, pages + idx, prev_shift); > + > +out: > + flush_cache_vmap(start, end); > + return err; > +} > + > /** > * vmap - map an array of pages into virtually contiguous space > * @pages: array of page pointers > @@ -3588,8 +3671,8 @@ void *vmap(struct page **pages, unsigned int count, > return NULL; > > addr = (unsigned long)area->addr; > - if (vmap_pages_range(addr, addr + size, pgprot_nx(prot), > - pages, PAGE_SHIFT) < 0) { > + if (vmap_batched(addr, addr + size, pgprot_nx(prot), > + pages) < 0) { > Better naming? vmap_pages_range_batched()? -- Uladzislau Rezki