linux-kernel - Re: [PATCH v4 1/2] mm/vmalloc: add vmalloc_no

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Date:   Mon, 14 Jun 2021 15:55:30 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, frankja@...ux.ibm.com,
        borntraeger@...ibm.com, cohuck@...hat.com, linux-mm@...ck.org,
        Uladzislau Rezki <urezki@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v4 1/2] mm/vmalloc: add vmalloc_no_huge

> On 14.06.21 15:23, Claudio Imbrenda wrote:
> > Commit 121e6f3258fe3 ("mm/vmalloc: hugepage vmalloc mappings") added
> > support for hugepage vmalloc mappings, it also added the flag
> > VM_NO_HUGE_VMAP for __vmalloc_node_range to request the allocation to
> > be performed with 0-order non-huge pages.  This flag is not accessible
> > when calling vmalloc, the only option is to call directly
> > __vmalloc_node_range, which is not exported.
> > 
> > This means that a module can't vmalloc memory with small pages.
> > 
> > Case in point: KVM on s390x needs to vmalloc a large area, and it needs
> > to be mapped with non-huge pages, because of a hardware limitation.
> > 
> > This patch adds the function vmalloc_no_huge, which works like vmalloc,
> > but it is guaranteed to always back the mapping using small pages. This
> > new function is exported, therefore it is usable by modules.
> > 
> > Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> > Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > Acked-by: Nicholas Piggin <npiggin@...il.com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Nicholas Piggin <npiggin@...il.com>
> > Cc: Uladzislau Rezki (Sony) <urezki@...il.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: David Rientjes <rientjes@...gle.com>
> > Cc: Christoph Hellwig <hch@...radead.org>
> > ---
> >   include/linux/vmalloc.h |  1 +
> >   mm/vmalloc.c            | 16 ++++++++++++++++
> >   2 files changed, 17 insertions(+)
> > 
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index 4d668abb6391..bfaaf0b6fa76 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -135,6 +135,7 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
> >   			const void *caller);
> >   void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
> >   		int node, const void *caller);
> > +void *vmalloc_no_huge(unsigned long size);
> >   extern void vfree(const void *addr);
> >   extern void vfree_atomic(const void *addr);
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index a13ac524f6ff..296a2fcc3fbe 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2998,6 +2998,22 @@ void *vmalloc(unsigned long size)
> >   }
> >   EXPORT_SYMBOL(vmalloc);
> > +/**
> > + * vmalloc_no_huge - allocate virtually contiguous memory using small pages
> > + * @size:    allocation size
> > + *
> > + * Allocate enough non-huge pages to cover @size from the page level
> > + * allocator and map them into contiguous kernel virtual space.
> > + *
> > + * Return: pointer to the allocated memory or %NULL on error
> > + */
> > +void *vmalloc_no_huge(unsigned long size)
> > +{
> > +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL,
> > +				    VM_NO_HUGE_VMAP, NUMA_NO_NODE, __builtin_return_address(0));
> > +}
> > +EXPORT_SYMBOL(vmalloc_no_huge);
> > +
> >   /**
> >    * vzalloc - allocate virtually contiguous memory with zero fill
> >    * @size:    allocation size
> > 
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
> 
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

--
Vlad Rezki