Re: [PATCH 01/35] fscache: Remove unused ->now_uncached callback

[Jan Kara]

On Thu 01-06-17 13:34:34, Jan Kara wrote:
> On Thu 01-06-17 11:26:08, David Howells wrote:
> > Jan Kara  wrote:
> > 
> > > The callback doesn't ever get called. Remove it.
> > 
> > Hmmm...  I should perhaps be calling this.  I'm not sure why I never did.
> > 
> > At the moment, it doesn't strictly matter as ops on pages marked with
> > PG_fscache get ignored if the cache has suffered an I/O error or has been
> > withdrawn - but it will incur a performance penalty (the PG_fscache flag is
> > checked in the netfs before calling into fscache).
> > 
> > The downside of calling this is that when a cache is removed, fscache would 
> > go
> > through all the cookies for that cache and iterate over all the pages
> > associated with those cookies - which could cause a performance dip in the
> > system.
> 
> So I know nothing about fscache. If you decide these functions should stay
> in as you are going to use them soon, then I can just convert them to the
> new API as everything else. What just caught my eye and why I had a more
> detailed look is that I didn't understand that 'PAGEVEC_SIZE -
> pagevec_count()' as a pagevec_lookup() argument since pagevec_count()
> should always return 0 at that point?

David, what is your final decision regarding this? Do you want to keep
these unused functions (and I will just update my patch to convert them to
the new calling convention) or will you apply the patch to remove them?

Honza
-- 
Jan Kara 
SUSE Labs, CR
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Re: [PATCH 01/35] fscache: Remove unused ->now_uncached callback

[Jan Kara]

On Thu 01-06-17 11:26:08, David Howells wrote:
> Jan Kara  wrote:
> 
> > The callback doesn't ever get called. Remove it.
> 
> Hmmm...  I should perhaps be calling this.  I'm not sure why I never did.
> 
> At the moment, it doesn't strictly matter as ops on pages marked with
> PG_fscache get ignored if the cache has suffered an I/O error or has been
> withdrawn - but it will incur a performance penalty (the PG_fscache flag is
> checked in the netfs before calling into fscache).
> 
> The downside of calling this is that when a cache is removed, fscache would go
> through all the cookies for that cache and iterate over all the pages
> associated with those cookies - which could cause a performance dip in the
> system.

So I know nothing about fscache. If you decide these functions should stay
in as you are going to use them soon, then I can just convert them to the
new API as everything else. What just caught my eye and why I had a more
detailed look is that I didn't understand that 'PAGEVEC_SIZE -
pagevec_count()' as a pagevec_lookup() argument since pagevec_count()
should always return 0 at that point?

Honza
-- 
Jan Kara 
SUSE Labs, CR
--
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Re: [PATCH 01/35] fscache: Remove unused ->now_uncached callback

[David Howells]

Jan Kara  wrote:

> The callback doesn't ever get called. Remove it.

Hmmm...  I should perhaps be calling this.  I'm not sure why I never did.

At the moment, it doesn't strictly matter as ops on pages marked with
PG_fscache get ignored if the cache has suffered an I/O error or has been
withdrawn - but it will incur a performance penalty (the PG_fscache flag is
checked in the netfs before calling into fscache).

The downside of calling this is that when a cache is removed, fscache would go
through all the cookies for that cache and iterate over all the pages
associated with those cookies - which could cause a performance dip in the
system.

David
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