On Thu, 1 Mar 2001, Roman Zippel wrote:
> Hi,
>
> On Thu, 1 Mar 2001, Alexander Viro wrote:
>
> > +static int generic_vm_expand(struct address_space *mapping, loff_t size)
> > +{
> > + struct page *page;
> > + unsigned long index, offset;
> > + int err;
> > +
> > + if (!mapping->a_ops->prepare_write || !mapping->a_ops->commit_write)
> > + return -ENOSYS;
> > +
> > + offset = (size & (PAGE_CACHE_SIZE-1)); /* Within page */
> > + index = size >> PAGE_CACHE_SHIFT;
>
> For affs I did basically the same with a small difference:
>
> offset = ((size-1) & (PAGE_CACHE_SIZE-1)) + 1;
> index = (size-1) >> PAGE_CACHE_SHIFT;
>
> That works fine here and allocates a page in the cache more likely to be
> used.
The only difference is in the case when size is a multiple of
PAGE_CACHE_SHIFT, so most of the time it's the same, but yeah, this
variant is probably nicer.
The problem with putting it into ->truncate() is obvious -
handling errors. And doing the thing before vmtruncate() (in
foo_notify_change(), whatever) is also PITA - you need to
reproduce the rlimit handling. Not nice...
IOW, if it's worth doing at all it probably should be
on expanding path in vmtruncate() - limit checks are already
done, but old i_size is still not lost...
Cheers,
Al
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This archive was generated by hypermail 2b29 : Wed Mar 07 2001 - 21:00:10 EST