* [PATCH v2] arm64/mm: add fallback option to allocate virtually @ 2020-09-30 23:13 Sudarshan Rajagopalan 2020-09-30 23:13 ` [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory Sudarshan Rajagopalan 0 siblings, 1 reply; 4+ messages in thread From: Sudarshan Rajagopalan @ 2020-09-30 23:13 UTC (permalink / raw) To: linux-arm-kernel, linux-kernel; +Cc: Sudarshan Rajagopalan V1: The initial patch used the approach to abort at the first instance of PMD_SIZE allocation failure, unmaps all previously mapped sections using vmemmap_free and maps the entire request with vmemmap_populate_basepages to allocate virtually contiguous memory. https://lkml.org/lkml/2020/9/10/66 V2: Allocates virtually contiguous memory only for sections that failed PMD_SIZE allocation, and continues to allocate physically contiguous memory for other sections. Sudarshan Rajagopalan (1): arm64/mm: add fallback option to allocate virtually contiguous memory arch/arm64/mm/mmu.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory 2020-09-30 23:13 [PATCH v2] arm64/mm: add fallback option to allocate virtually Sudarshan Rajagopalan @ 2020-09-30 23:13 ` Sudarshan Rajagopalan 2020-10-01 0:30 ` Anshuman Khandual 0 siblings, 1 reply; 4+ messages in thread From: Sudarshan Rajagopalan @ 2020-09-30 23:13 UTC (permalink / raw) To: linux-arm-kernel, linux-kernel Cc: Mark Rutland, Will Deacon, Anshuman Khandual, Catalin Marinas, Sudarshan Rajagopalan, David Hildenbrand, Steven Price, Andrew Morton, Logan Gunthorpe When section mappings are enabled, we allocate vmemmap pages from physically continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). Section mappings are good to reduce TLB pressure. But when system is highly fragmented and memory blocks are being hot-added at runtime, its possible that such physically continuous memory allocations can fail. Rather than failing the memory hot-add procedure, add a fallback option to allocate vmemmap pages from discontinuous pages using vmemmap_populate_basepages(). Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Logan Gunthorpe <logang@deltatee.com> Cc: David Hildenbrand <david@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Steven Price <steven.price@arm.com> --- arch/arm64/mm/mmu.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 75df62f..9edbbb8 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1121,8 +1121,18 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, void *p = NULL; p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); - if (!p) - return -ENOMEM; + if (!p) { + if (altmap) + return -ENOMEM; /* no fallback */ + + /* + * fallback allocating with virtually + * contiguous memory for this section + */ + if (vmemmap_populate_basepages(addr, next, node, NULL)) + return -ENOMEM; + continue; + } pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL)); } else -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory 2020-09-30 23:13 ` [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory Sudarshan Rajagopalan @ 2020-10-01 0:30 ` Anshuman Khandual 2020-10-01 19:51 ` Sudarshan Rajagopalan 0 siblings, 1 reply; 4+ messages in thread From: Anshuman Khandual @ 2020-10-01 0:30 UTC (permalink / raw) To: Sudarshan Rajagopalan, linux-arm-kernel, linux-kernel Cc: Mark Rutland, Will Deacon, David Hildenbrand, Catalin Marinas, Steven Price, Andrew Morton, Logan Gunthorpe On 10/01/2020 04:43 AM, Sudarshan Rajagopalan wrote: > When section mappings are enabled, we allocate vmemmap pages from physically > continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). Section > mappings are good to reduce TLB pressure. But when system is highly fragmented > and memory blocks are being hot-added at runtime, its possible that such > physically continuous memory allocations can fail. Rather than failing the > memory hot-add procedure, add a fallback option to allocate vmemmap pages from > discontinuous pages using vmemmap_populate_basepages(). > > Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Logan Gunthorpe <logang@deltatee.com> > Cc: David Hildenbrand <david@redhat.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Steven Price <steven.price@arm.com> > --- > arch/arm64/mm/mmu.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 75df62f..9edbbb8 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1121,8 +1121,18 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > void *p = NULL; > > p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); > - if (!p) > - return -ENOMEM; > + if (!p) { > + if (altmap) > + return -ENOMEM; /* no fallback */ Why ? If huge pages inside a vmemmap section might have been allocated from altmap, the base page could also fallback on altmap. If this patch has just followed the existing x86 semantics, it was written [1] long back before vmemmap_populate_basepages() supported altmap allocation. While adding that support [2] recently, it was deliberate not to change x86 semantics as it was a platform decision. Nonetheless, it makes sense to fallback on altmap bases pages if and when required. [1] 4b94ffdc4163 (x86, mm: introduce vmem_altmap to augment vmemmap_populate()) [2] 1d9cfee7535c (mm/sparsemem: enable vmem_altmap support in vmemmap_populate_basepages()) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory 2020-10-01 0:30 ` Anshuman Khandual @ 2020-10-01 19:51 ` Sudarshan Rajagopalan 0 siblings, 0 replies; 4+ messages in thread From: Sudarshan Rajagopalan @ 2020-10-01 19:51 UTC (permalink / raw) To: Anshuman Khandual Cc: Mark Rutland, Will Deacon, David Hildenbrand, Catalin Marinas, linux-kernel, Steven Price, Andrew Morton, Logan Gunthorpe, linux-arm-kernel On 2020-09-30 17:30, Anshuman Khandual wrote: > On 10/01/2020 04:43 AM, Sudarshan Rajagopalan wrote: >> When section mappings are enabled, we allocate vmemmap pages from >> physically >> continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). >> Section >> mappings are good to reduce TLB pressure. But when system is highly >> fragmented >> and memory blocks are being hot-added at runtime, its possible that >> such >> physically continuous memory allocations can fail. Rather than failing >> the >> memory hot-add procedure, add a fallback option to allocate vmemmap >> pages from >> discontinuous pages using vmemmap_populate_basepages(). >> >> Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Anshuman Khandual <anshuman.khandual@arm.com> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Logan Gunthorpe <logang@deltatee.com> >> Cc: David Hildenbrand <david@redhat.com> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> Cc: Steven Price <steven.price@arm.com> >> --- >> arch/arm64/mm/mmu.c | 14 ++++++++++++-- >> 1 file changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index 75df62f..9edbbb8 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -1121,8 +1121,18 @@ int __meminit vmemmap_populate(unsigned long >> start, unsigned long end, int node, >> void *p = NULL; >> >> p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); >> - if (!p) >> - return -ENOMEM; >> + if (!p) { >> + if (altmap) >> + return -ENOMEM; /* no fallback */ > > Why ? If huge pages inside a vmemmap section might have been allocated > from altmap, the base page could also fallback on altmap. If this patch > has just followed the existing x86 semantics, it was written [1] long > back before vmemmap_populate_basepages() supported altmap allocation. > While adding that support [2] recently, it was deliberate not to change > x86 semantics as it was a platform decision. Nonetheless, it makes > sense > to fallback on altmap bases pages if and when required. > > [1] 4b94ffdc4163 (x86, mm: introduce vmem_altmap to augment > vmemmap_populate()) > [2] 1d9cfee7535c (mm/sparsemem: enable vmem_altmap support in > vmemmap_populate_basepages()) Yes agreed. We can allow fallback on altmap as well. I did indeed follow x86 semantics. Will send the updated patch. Sudarshan -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 4+ messages in thread
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