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Peter Anvin" , Ingo Molnar , Linus Torvalds , =?utf-8?Q?=C5=81ukasz?= Majczak , Mel Gorman , Michal Hocko , Qian Cai , "Sarvela, Tomi P" , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout Message-ID: <20210225180521.GH1854360@linux.ibm.com> References: <20210224153950.20789-1-rppt@kernel.org> <20210224153950.20789-2-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-02-25_10:2021-02-24,2021-02-25 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 clxscore=1015 mlxscore=0 impostorscore=0 malwarescore=0 priorityscore=1501 suspectscore=0 adultscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102250138 X-Stat-Signature: st9jcoet78ceexq6zqyh49bsxjsntu9q X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A1E552000DBE Received-SPF: none (linux.ibm.com>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=mx0a-001b2d01.pphosted.com; client-ip=148.163.156.1 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614276340-816307 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote: > On 2/24/21 4:39 PM, Mike Rapoport wrote: > > From: Mike Rapoport > > Hi, thanks for your efforts. I'll just nit pick on the description/comments as I > don't feel confident about judging the implementation correctness, sorry :) > > > There could be struct pages that are not backed by actual physical memory. > > This can happen when the actual memory bank is not a multiple of > > SECTION_SIZE or when an architecture does not register memory holes > > reserved by the firmware as memblock.memory. > > > > Such pages are currently initialized using init_unavailable_mem() function > > that iterates through PFNs in holes in memblock.memory and if there is a > > struct page corresponding to a PFN, the fields of this page are set to > > default values and it is marked as Reserved. > > > > init_unavailable_mem() does not take into account zone and node the page > > belongs to and sets both zone and node links in struct page to zero. > > > > Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions > > rather that check each PFN") the holes inside a zone were re-initialized > > during memmap_init() and got their zone/node links right. However, after > > that commit nothing updates the struct pages representing such holes. > > > > On a system that has firmware reserved holes in a zone above ZONE_DMA, for > > instance in a configuration below: > > > > # grep -A1 E820 /proc/iomem > > 7a17b000-7a216fff : Unknown E820 type > > 7a217000-7bffffff : System RAM > > > > unset zone link in struct page will trigger > > > > VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); > > ... in set_pfnblock_flags_mask() when called with a struct page from the > "Unknown E820 type" range. "... in set_pfnblock_flags_mask() when called with a struct page from a range other than E820_TYPE_RAM" then :) > > because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link > > in struct page) in the same pageblock. > > I would say "there are apparently pages" ... "and ZONE_DMA does not span this range" I'd rephrase it differently, something like "because there are pages in the range of ZONE_DMA32 but the unset zone link in struct page makes them appear as a part of ZONE_DMA" > > Interleave initialization of the unavailable pages with the normal > > initialization of memory map, so that zone and node information will be > > properly set on struct pages that are not backed by the actual memory. > > > > With this change the pages for holes inside a zone will get proper > > zone/node links and the pages that are not spanned by any node will get > > links to the adjacent zone/node. > > What if two zones are adjacent? I.e. if the hole was at a boundary between two > zones. What do you mean by "adjacent zones"? If there is a hole near the zone boundary, zone span would be clamped to exclude the hole. > > Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") > > Signed-off-by: Mike Rapoport > > Reported-by: Qian Cai > > Reported-by: Andrea Arcangeli > > Reviewed-by: Baoquan He > > For the approach: > Acked-by: Vlastimil Babka > > > --- > > mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- > > 1 file changed, 64 insertions(+), 83 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 3e93f8b29bae..a11a9acde708 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) > > } > > } > > > > +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) > > +/* > > + * Only struct pages that correspond to ranges defined by memblock.memory > > + * are zeroed and initialized by going through __init_single_page() during > > + * memmap_init_zone(). > > + * > > + * But, there could be struct pages that correspond to holes in > > + * memblock.memory. This can happen because of the following reasons: > > + * - phyiscal memory bank size is not necessarily the exact multiple of the > > physical Thanks. > > + * arbitrary section size > > + * - early reserved memory may not be listed in memblock.memory > > + * - memory layouts defined with memmap= kernel parameter may not align > > + * nicely with memmap sections > > + * > > + * Explicitly initialize those struct pages so that: > > + * - PG_Reserved is set > > + * - zone and node links point to zone and node that span the page > > Yes spanned pages are the most important, but should you also describe here the > adjacent ones, as you do in commit log? Will try :) > > + */ > > +static u64 __meminit init_unavailable_range(unsigned long spfn, > > + unsigned long epfn, > > + int zone, int node) > > +{ > > + unsigned long pfn; > > + u64 pgcnt = 0; > > + > > + for (pfn = spfn; pfn < epfn; pfn++) { > > + if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) { > > + pfn = ALIGN_DOWN(pfn, pageblock_nr_pages) > > + + pageblock_nr_pages - 1; > > + continue; > > + } > > + __init_single_page(pfn_to_page(pfn), pfn, zone, node); > > + __SetPageReserved(pfn_to_page(pfn)); > > + pgcnt++; > > + } > > + > > + return pgcnt; > > +} > > +#else > > +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn, > > + int zone, int node) > > +{ > > + return 0; > > +} > > +#endif > > + > > void __meminit __weak memmap_init_zone(struct zone *zone) > > { > > unsigned long zone_start_pfn = zone->zone_start_pfn; > > unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; > > int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone); > > + static unsigned long hole_pfn = 0; > > unsigned long start_pfn, end_pfn; > > + u64 pgcnt = 0; > > > > for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { > > start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); > > @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) > > memmap_init_range(end_pfn - start_pfn, nid, > > zone_id, start_pfn, zone_end_pfn, > > MEMINIT_EARLY, NULL, MIGRATE_MOVABLE); > > + > > + if (hole_pfn < start_pfn) > > + pgcnt += init_unavailable_range(hole_pfn, start_pfn, > > + zone_id, nid); > > + hole_pfn = end_pfn; > > } > > + > > +#ifdef CONFIG_SPARSEMEM > > + end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION); > > + if (hole_pfn < end_pfn) > > + pgcnt += init_unavailable_range(hole_pfn, end_pfn, > > + zone_id, nid); > > +#endif > > + > > + if (pgcnt) > > + pr_info(" %s zone: %lld pages in unavailable ranges\n", > > + zone->name, pgcnt); > > } > > > > static int zone_batchsize(struct zone *zone) > > @@ -7092,88 +7156,6 @@ void __init free_area_init_memoryless_node(int nid) > > free_area_init_node(nid); > > } > > > > -#if !defined(CONFIG_FLAT_NODE_MEM_MAP) > > -/* > > - * Initialize all valid struct pages in the range [spfn, epfn) and mark them > > - * PageReserved(). Return the number of struct pages that were initialized. > > - */ > > -static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn) > > -{ > > - unsigned long pfn; > > - u64 pgcnt = 0; > > - > > - for (pfn = spfn; pfn < epfn; pfn++) { > > - if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) { > > - pfn = ALIGN_DOWN(pfn, pageblock_nr_pages) > > - + pageblock_nr_pages - 1; > > - continue; > > - } > > - /* > > - * Use a fake node/zone (0) for now. Some of these pages > > - * (in memblock.reserved but not in memblock.memory) will > > - * get re-initialized via reserve_bootmem_region() later. > > - */ > > - __init_single_page(pfn_to_page(pfn), pfn, 0, 0); > > - __SetPageReserved(pfn_to_page(pfn)); > > - pgcnt++; > > - } > > - > > - return pgcnt; > > -} > > - > > -/* > > - * Only struct pages that are backed by physical memory are zeroed and > > - * initialized by going through __init_single_page(). But, there are some > > - * struct pages which are reserved in memblock allocator and their fields > > - * may be accessed (for example page_to_pfn() on some configuration accesses > > - * flags). We must explicitly initialize those struct pages. > > - * > > - * This function also addresses a similar issue where struct pages are left > > - * uninitialized because the physical address range is not covered by > > - * memblock.memory or memblock.reserved. That could happen when memblock > > - * layout is manually configured via memmap=, or when the highest physical > > - * address (max_pfn) does not end on a section boundary. > > - */ > > -static void __init init_unavailable_mem(void) > > -{ > > - phys_addr_t start, end; > > - u64 i, pgcnt; > > - phys_addr_t next = 0; > > - > > - /* > > - * Loop through unavailable ranges not covered by memblock.memory. > > - */ > > - pgcnt = 0; > > - for_each_mem_range(i, &start, &end) { > > - if (next < start) > > - pgcnt += init_unavailable_range(PFN_DOWN(next), > > - PFN_UP(start)); > > - next = end; > > - } > > - > > - /* > > - * Early sections always have a fully populated memmap for the whole > > - * section - see pfn_valid(). If the last section has holes at the > > - * end and that section is marked "online", the memmap will be > > - * considered initialized. Make sure that memmap has a well defined > > - * state. > > - */ > > - pgcnt += init_unavailable_range(PFN_DOWN(next), > > - round_up(max_pfn, PAGES_PER_SECTION)); > > - > > - /* > > - * Struct pages that do not have backing memory. This could be because > > - * firmware is using some of this memory, or for some other reasons. > > - */ > > - if (pgcnt) > > - pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt); > > -} > > -#else > > -static inline void __init init_unavailable_mem(void) > > -{ > > -} > > -#endif /* !CONFIG_FLAT_NODE_MEM_MAP */ > > - > > #if MAX_NUMNODES > 1 > > /* > > * Figure out the number of possible node ids. > > @@ -7597,7 +7579,6 @@ void __init free_area_init(unsigned long *max_zone_pfn) > > /* Initialise every node */ > > mminit_verify_pageflags_layout(); > > setup_nr_node_ids(); > > - init_unavailable_mem(); > > for_each_online_node(nid) { > > pg_data_t *pgdat = NODE_DATA(nid); > > free_area_init_node(nid); > > > -- Sincerely yours, Mike.