Re: [PATCH] Add notification of page becoming writable to VMA ops [try #3]

[Miklos Szeredi <miklos@szeredi.hu>]

> The attached patch adds a new VMA operation to notify a filesystem or other
> driver about the MMU generating a fault because userspace attempted to write
> to a page mapped through a read-only PTE.
> 
> This facility permits the filesystem or driver to:
> 
>  (*) Implement storage allocation/reservation on attempted write, and so to
>      deal with problems such as ENOSPC more gracefully (perhaps by generating
>      SIGBUS).
> 
>  (*) Delay making the page writable until the contents have been written to a
>      backing cache. This is useful for NFS/AFS when using FS-Cache/CacheFS.
>      It permits the filesystem to have some guarantee about the state of the
>      cache.

  (*) account and limit number of dirty pages

This is one piece of the puzze needed to make shared writable mapping
work safely in FUSE.

> Updated to 2.6.14-git14.

But doesn't apply against 2.6.15-rc3 or -rc3-mm1.

Miklos
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