| Message ID | 20250418162727.1535335-1-lrh2000@pku.edu.cn (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/mm_init: Don't iterate pages below ARCH_PFN_OFFSET | expand |
On Sat, Apr 19, 2025 at 12:27:27AM +0800, Ruihan Li wrote: > Currently, memmap_init initializes pfn_hole with 0 instead of > ARCH_PFN_OFFSET. Then init_unavailable_range will start iterating each > page from the page at address zero to the first available page, but it > won't do anything for pages below ARCH_PFN_OFFSET because pfn_valid > won't pass. > > If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the > kernel is used as a library and loaded at a very high address), the > pointless iteration for pages below ARCH_PFN_OFFSET will take a very > long time, and the kernel will look stuck at boot time. > > This commit sets the initial value of pfn_hole to ARCH_PFN_OFFSET, which > avoids the problematic and useless iteration mentioned above. > > Fixes: 907ec5fca3dc ("mm: zero remaining unavailable struct pages") I don't think it should be backported, this does not fix a bug. > Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn> > --- > mm/mm_init.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 84f14fa12..b3ae9f797 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -966,7 +966,7 @@ static void __init memmap_init_zone_range(struct zone *zone, > static void __init memmap_init(void) > { > unsigned long start_pfn, end_pfn; > - unsigned long hole_pfn = 0; > + unsigned long hole_pfn = ARCH_PFN_OFFSET; ARCH_PFN_OFFSET is defined only for FLATMEM, this won't even build for SPARSEMEM. > int i, j, zone_id = 0, nid; > > for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) { > -- > 2.49.0 > >
Hi Ruihan, kernel test robot noticed the following build errors: [auto build test ERROR on akpm-mm/mm-everything] url: https://github.com/intel-lab-lkp/linux/commits/Ruihan-Li/mm-mm_init-Don-t-iterate-pages-below-ARCH_PFN_OFFSET/20250419-002910 base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything patch link: https://lore.kernel.org/r/20250418162727.1535335-1-lrh2000%40pku.edu.cn patch subject: [PATCH] mm/mm_init: Don't iterate pages below ARCH_PFN_OFFSET config: s390-randconfig-002-20250419 (https://download.01.org/0day-ci/archive/20250419/202504191858.5WVRkO7O-lkp@intel.com/config) compiler: s390-linux-gcc (GCC) 7.5.0 reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250419/202504191858.5WVRkO7O-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202504191858.5WVRkO7O-lkp@intel.com/ All errors (new ones prefixed by >>): mm/mm_init.c: In function 'memmap_init': >> mm/mm_init.c:975:27: error: 'ARCH_PFN_OFFSET' undeclared (first use in this function); did you mean 'PREEMPT_OFFSET'? unsigned long hole_pfn = ARCH_PFN_OFFSET; ^~~~~~~~~~~~~~~ PREEMPT_OFFSET mm/mm_init.c:975:27: note: each undeclared identifier is reported only once for each function it appears in vim +975 mm/mm_init.c 971 972 static void __init memmap_init(void) 973 { 974 unsigned long start_pfn, end_pfn; > 975 unsigned long hole_pfn = ARCH_PFN_OFFSET; 976 int i, j, zone_id = 0, nid; 977 978 for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) { 979 struct pglist_data *node = NODE_DATA(nid); 980 981 for (j = 0; j < MAX_NR_ZONES; j++) { 982 struct zone *zone = node->node_zones + j; 983 984 if (!populated_zone(zone)) 985 continue; 986 987 memmap_init_zone_range(zone, start_pfn, end_pfn, 988 &hole_pfn); 989 zone_id = j; 990 } 991 } 992 993 /* 994 * Initialize the memory map for hole in the range [memory_end, 995 * section_end] for SPARSEMEM and in the range [memory_end, memmap_end] 996 * for FLATMEM. 997 * Append the pages in this hole to the highest zone in the last 998 * node. 999 */ 1000 #ifdef CONFIG_SPARSEMEM 1001 end_pfn = round_up(end_pfn, PAGES_PER_SECTION); 1002 #else 1003 end_pfn = round_up(end_pfn, MAX_ORDER_NR_PAGES); 1004 #endif 1005 if (hole_pfn < end_pfn) 1006 init_unavailable_range(hole_pfn, end_pfn, zone_id, nid); 1007 } 1008
Hi Ruihan, kernel test robot noticed the following build errors: [auto build test ERROR on akpm-mm/mm-everything] url: https://github.com/intel-lab-lkp/linux/commits/Ruihan-Li/mm-mm_init-Don-t-iterate-pages-below-ARCH_PFN_OFFSET/20250419-002910 base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything patch link: https://lore.kernel.org/r/20250418162727.1535335-1-lrh2000%40pku.edu.cn patch subject: [PATCH] mm/mm_init: Don't iterate pages below ARCH_PFN_OFFSET config: s390-randconfig-001-20250419 (https://download.01.org/0day-ci/archive/20250419/202504191834.zUYILN1L-lkp@intel.com/config) compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project f819f46284f2a79790038e1f6649172789734ae8) reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250419/202504191834.zUYILN1L-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202504191834.zUYILN1L-lkp@intel.com/ All errors (new ones prefixed by >>): >> mm/mm_init.c:975:27: error: use of undeclared identifier 'ARCH_PFN_OFFSET' 975 | unsigned long hole_pfn = ARCH_PFN_OFFSET; | ^ 1 error generated. vim +/ARCH_PFN_OFFSET +975 mm/mm_init.c 971 972 static void __init memmap_init(void) 973 { 974 unsigned long start_pfn, end_pfn; > 975 unsigned long hole_pfn = ARCH_PFN_OFFSET; 976 int i, j, zone_id = 0, nid; 977 978 for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) { 979 struct pglist_data *node = NODE_DATA(nid); 980 981 for (j = 0; j < MAX_NR_ZONES; j++) { 982 struct zone *zone = node->node_zones + j; 983 984 if (!populated_zone(zone)) 985 continue; 986 987 memmap_init_zone_range(zone, start_pfn, end_pfn, 988 &hole_pfn); 989 zone_id = j; 990 } 991 } 992 993 /* 994 * Initialize the memory map for hole in the range [memory_end, 995 * section_end] for SPARSEMEM and in the range [memory_end, memmap_end] 996 * for FLATMEM. 997 * Append the pages in this hole to the highest zone in the last 998 * node. 999 */ 1000 #ifdef CONFIG_SPARSEMEM 1001 end_pfn = round_up(end_pfn, PAGES_PER_SECTION); 1002 #else 1003 end_pfn = round_up(end_pfn, MAX_ORDER_NR_PAGES); 1004 #endif 1005 if (hole_pfn < end_pfn) 1006 init_unavailable_range(hole_pfn, end_pfn, zone_id, nid); 1007 } 1008
Hi Mike, Thanks a lot for your review! On Sat, Apr 19, 2025 at 10:16:34AM +0300, Mike Rapoport wrote: > On Sat, Apr 19, 2025 at 12:27:27AM +0800, Ruihan Li wrote: > > Currently, memmap_init initializes pfn_hole with 0 instead of > > ARCH_PFN_OFFSET. Then init_unavailable_range will start iterating each > > page from the page at address zero to the first available page, but it > > won't do anything for pages below ARCH_PFN_OFFSET because pfn_valid > > won't pass. > > > > If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the > > kernel is used as a library and loaded at a very high address), the > > pointless iteration for pages below ARCH_PFN_OFFSET will take a very > > long time, and the kernel will look stuck at boot time. > > > > This commit sets the initial value of pfn_hole to ARCH_PFN_OFFSET, which > > avoids the problematic and useless iteration mentioned above. > > > > Fixes: 907ec5fca3dc ("mm: zero remaining unavailable struct pages") > > I don't think it should be backported, this does not fix a bug. I thought the Fixes tag only indicated that the problem existed since the specific commit, not the need for a backport (since the backport should only happen when someone sends or CC's the patch to the linux-stable mailing list)? But anyway, I'm going to remove the Fixes tag when I send v2. > > > Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn> > > --- > > mm/mm_init.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/mm_init.c b/mm/mm_init.c > > index 84f14fa12..b3ae9f797 100644 > > --- a/mm/mm_init.c > > +++ b/mm/mm_init.c > > @@ -966,7 +966,7 @@ static void __init memmap_init_zone_range(struct zone *zone, > > static void __init memmap_init(void) > > { > > unsigned long start_pfn, end_pfn; > > - unsigned long hole_pfn = 0; > > + unsigned long hole_pfn = ARCH_PFN_OFFSET; > > ARCH_PFN_OFFSET is defined only for FLATMEM, this won't even build for > SPARSEMEM. Sorry for my ignorance. I'm not familiar with the code and I'm only testing the FLATMEM configuration. I'll send a v2 patch to fix this. Thanks for pointing out my stupid mistake. > > > int i, j, zone_id = 0, nid; > > > > for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) { > > -- > > 2.49.0 > > > > > > -- > Sincerely yours, > Mike. Thanks, Ruihan Li
diff --git a/mm/mm_init.c b/mm/mm_init.c index 84f14fa12..b3ae9f797 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -966,7 +966,7 @@ static void __init memmap_init_zone_range(struct zone *zone, static void __init memmap_init(void) { unsigned long start_pfn, end_pfn; - unsigned long hole_pfn = 0; + unsigned long hole_pfn = ARCH_PFN_OFFSET; int i, j, zone_id = 0, nid; for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
Currently, memmap_init initializes pfn_hole with 0 instead of ARCH_PFN_OFFSET. Then init_unavailable_range will start iterating each page from the page at address zero to the first available page, but it won't do anything for pages below ARCH_PFN_OFFSET because pfn_valid won't pass. If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the kernel is used as a library and loaded at a very high address), the pointless iteration for pages below ARCH_PFN_OFFSET will take a very long time, and the kernel will look stuck at boot time. This commit sets the initial value of pfn_hole to ARCH_PFN_OFFSET, which avoids the problematic and useless iteration mentioned above. Fixes: 907ec5fca3dc ("mm: zero remaining unavailable struct pages") Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn> --- mm/mm_init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)