Re: [RFC][PATCH] tracking dirty pages in shared mappings

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Sat, 2006-05-06 at 23:18 +1000, Nick Piggin wrote:

> 
> Looks pretty good. Christoph and I were looking at ways to improve
> performance impact of this, and skipping the extra work for particular
> (eg. shmem) mappings might be a good idea?
> 
> Attached is a patch with a couple of things I've currently got.

will merge with mine and post a new version shortly.

> In the long run, I'd like to be able to set_page_dirty and
> balance_dirty_pages outside of both ptl and mmap_sem, for performance
> reasons. That will require a reworking of arch code though :(

That would indeed be very nice if possible.

> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h	2006-05-06 23:05:10.000000000 +1000
> +++ linux-2.6/include/linux/mm.h	2006-05-06 23:06:17.000000000 +1000
> @@ -183,8 +183,7 @@ extern unsigned int kobjsize(const void 
>  #define VM_SequentialReadHint(v)	((v)->vm_flags & VM_SEQ_READ)
>  #define VM_RandomReadHint(v)		((v)->vm_flags & VM_RAND_READ)
>  
> -#define VM_SharedWritable(v)		(((v)->vm_flags & (VM_SHARED | VM_MAYSHARE)) && \
> -					 ((v)->vm_flags & VM_WRITE))
> +#define VM_SharedWritable(v)		((v)->vm_flags & (VM_SHARED|VM_WRITE))
>  
>  /*
>   * mapping from the currently active vm_flags protection bits (the

That doesn't look right, your version is true even for unwritable
shared, and writable non-shared VMAs.

PeterZ

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