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Date: Wed, 10 Mar 2021 11:37:53 +0530
From: Naresh Kamboju <naresh.kamboju@...aro.org>
To: Oscar Salvador <osalvador@...e.de>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Linux-Next Mailing List <linux-next@...r.kernel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
X86 ML <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
Michal Hocko <mhocko@...nel.org>, Zi Yan <ziy@...dia.com>,
linux-mm <linux-mm@...ck.org>,
open list <linux-kernel@...r.kernel.org>,
lkft-triage@...ts.linaro.org,
Stephen Rothwell <sfr@...b.auug.org.au>,
Arnd Bergmann <arnd@...db.de>,
Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v6 3/4] x86/vmemmap: Handle unpopulated sub-pmd ranges
Hi Oscar,
On Wed, 10 Mar 2021 at 03:11, Oscar Salvador <osalvador@...e.de> wrote:
>
> When sizeof(struct page) is not a power of 2, sections do not span
> a PMD anymore and so when populating them some parts of the PMD will
> remain unused.
> Because of this, PMDs will be left behind when depopulating sections
> since remove_pmd_table() thinks that those unused parts are still in
> use.
>
> Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
> will do the right thing and will let us free the PMD when the last user
> of it is gone.
>
> This patch is based on a similar patch by David Hildenbrand:
>
> https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
> arch/x86/mm/init_64.c | 65 +++++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 53 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 9ecb3c488ac8..d93b36856ed3 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -826,6 +826,51 @@ void __init paging_init(void)
> zone_sizes_init();
> }
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> +#define PAGE_UNUSED 0xFD
> +
> +/* Returns true if the PMD is completely unused and thus it can be freed */
> +static bool __meminit vmemmap_pmd_is_unused(unsigned long addr, unsigned long end)
> +{
> + unsigned long start = ALIGN_DOWN(addr, PMD_SIZE);
> +
> + memset((void *)addr, PAGE_UNUSED, end - addr);
> +
> + return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE);
> +}
> +
> +static void __meminit vmemmap_use_sub_pmd(unsigned long start)
> +{
> + /*
> + * As we expect to add in the same granularity as we remove, it's
> + * sufficient to mark only some piece used to block the memmap page from
> + * getting removed when removing some other adjacent memmap (just in
> + * case the first memmap never gets initialized e.g., because the memory
> + * block never gets onlined).
> + */
> + memset((void *)start, 0, sizeof(struct page));
> +}
> +
> +static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)
> +{
> + /*
> + * Could be our memmap page is filled with PAGE_UNUSED already from a
> + * previous remove. Make sure to reset it.
> + */
> + vmemmap_use_sub_pmd(start);
> +
> + /*
> + * Mark with PAGE_UNUSED the unused parts of the new memmap range
> + */
> + if (!IS_ALIGNED(start, PMD_SIZE))
> + memset((void *)start, PAGE_UNUSED,
> + start - ALIGN_DOWN(start, PMD_SIZE));
> + if (!IS_ALIGNED(end, PMD_SIZE))
> + memset((void *)end, PAGE_UNUSED,
> + ALIGN(end, PMD_SIZE) - end);
> +}
> +#endif
> +
> /*
> * Memory hotplug specific functions
> */
> @@ -871,8 +916,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
> return add_pages(nid, start_pfn, nr_pages, params);
> }
>
> -#define PAGE_INUSE 0xFD
> -
> static void __meminit free_pagetable(struct page *page, int order)
> {
> unsigned long magic;
> @@ -1006,7 +1049,6 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> unsigned long next, pages = 0;
> pte_t *pte_base;
> pmd_t *pmd;
> - void *page_addr;
>
> pmd = pmd_start + pmd_index(addr);
> for (; addr < end; addr = next, pmd++) {
> @@ -1026,20 +1068,13 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> pmd_clear(pmd);
> spin_unlock(&init_mm.page_table_lock);
> pages++;
> - } else {
> - /* If here, we are freeing vmemmap pages. */
> - memset((void *)addr, PAGE_INUSE, next - addr);
> -
> - page_addr = page_address(pmd_page(*pmd));
> - if (!memchr_inv(page_addr, PAGE_INUSE,
> - PMD_SIZE)) {
> + } else if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
> + vmemmap_pmd_is_unused(addr, next)) {
> free_hugepage_table(pmd_page(*pmd),
> altmap);
> -
> spin_lock(&init_mm.page_table_lock);
> pmd_clear(pmd);
> spin_unlock(&init_mm.page_table_lock);
> - }
> }
>
> continue;
> @@ -1492,11 +1527,17 @@ static int __meminit vmemmap_populate_hugepages(unsigned long start,
>
> addr_end = addr + PMD_SIZE;
> p_end = p + PMD_SIZE;
> +
> + if (!IS_ALIGNED(addr, PMD_SIZE) ||
> + !IS_ALIGNED(next, PMD_SIZE))
> + vmemmap_use_new_sub_pmd(addr, next);
> +
> continue;
> } else if (altmap)
> return -ENOMEM; /* no fallback */
> } else if (pmd_large(*pmd)) {
> vmemmap_verify((pte_t *)pmd, node, addr, next);
> + vmemmap_use_sub_pmd(addr);
While building the linux next 20210310 tag for x86_64 architecture with clang-12
and gcc-9 the following warnings / errors were noticed.
arch/x86/mm/init_64.c:1585:6: error: implicit declaration of function
'vmemmap_use_new_sub_pmd' [-Werror,-Wimplicit-function-declaration]
vmemmap_use_new_sub_pmd(addr, next);
^
arch/x86/mm/init_64.c:1591:4: error: implicit declaration of function
'vmemmap_use_sub_pmd' [-Werror,-Wimplicit-function-declaration]
vmemmap_use_sub_pmd(addr, next);
^
2 errors generated.
make[3]: *** [scripts/Makefile.build:271: arch/x86/mm/init_64.o] Error 1
Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
Steps to reproduce:
-------------------
# TuxMake is a command line tool and Python library that provides
# portable and repeatable Linux kernel builds across a variety of
# architectures, toolchains, kernel configurations, and make targets.
#
# TuxMake supports the concept of runtimes.
# See https://docs.tuxmake.org/runtimes/, for that to work it requires
# that you install podman or docker on your system.
#
# To install tuxmake on your system globally:
# sudo pip3 install -U tuxmake
#
# See https://docs.tuxmake.org/ for complete documentation.
tuxmake --runtime podman --target-arch x86_64 --toolchain clang-12
--kconfig defconfig --kconfig-add
https://builds.tuxbuild.com/1pYCPt4WlgSfSdv1BULm6ABINeJ/config
Build pipeline error link,
https://gitlab.com/Linaro/lkft/mirrors/next/linux-next/-/jobs/1085496613#L428
--
Linaro LKFT
https://lkft.linaro.org
Download attachment "x86_64_next-20210310.config" of type "application/octet-stream" (137121 bytes)
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