On Monday 13 August 2007 02:18, Evgeniy Polyakov wrote:
> On Mon, Aug 13, 2007 at 02:08:57AM -0700, Daniel Phillips
([email protected]) wrote:
> > > But that idea fails as well, since reference counts and IO
> > > completion are two completely seperate entities. So unless end IO
> > > just happens to be the last user holding a reference to the bio,
> > > you cannot free it.
> >
> > That is not a problem. When bio_put hits zero it calls ->endio
> > instead of the destructor. The ->endio sees that the count is zero
> > and destroys the bio.
>
> This is not a very good solution, since it requires all users of the
> bios to know how to free it.
No, only the specific ->endio needs to know that, which is set by the
bio owner, so this knowledge lies in exactly the right place. A small
handful of generic endios all with the same destructor are used nearly
everywhere.
> Right now it is hidden.
> And adds additional atomic check (although reading is quite fast) in
> the end_io.
Actual endio happens once in the lifetime of the transfer, this read
will be entirely lost in the noise.
> And for what purpose? To eat 8 bytes on 64bit platform?
> This will not reduce its size noticebly, so the same number of bios
> will be in the cache's page, so what is a gain? All this cleanups and
> logic complicatins should be performed only if after size shring
> increased number of bios can fit into cache's page, will it be done
> after such cleanups?
Well, exactly, My point from the beginning was that the size of struct
bio is not even close to being a problem and adding a few bytes to it
in the interest of doing the cleanest fix to a core kernel bug is just
not a dominant issue.
I suppose that leaving out the word "bloated" and skipping straight to
the "doesn't matter" proof would have saved some bandwidth.
Regards,
Daniel
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