| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Cc: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, YUriy Zhuravlev <u(dot)zhuravlev(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Move PinBuffer and UnpinBuffer to atomics |
| Date: | 2016-03-28 13:09:04 |
| Message-ID: | 20160328130904.4mhugvkf4f3wg4qb@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2016-03-28 11:48:46 +0530, Dilip Kumar wrote:
> On Sun, Mar 27, 2016 at 5:48 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> >
> > What's sizeof(BufferDesc) after applying these patches? It should better
> > be <= 64...
> >
>
> It is 72.
Ah yes, miscalculated the required alignment. Hm. So we got to get this
smaller. I see three approaches:
1) Reduce the spinlock size on ppc. That actually might just work by
replacing "unsigned int" by "unsigned char"
2) Replace the lwlock spinlock by a bit in LWLock->state. That'd avoid
embedding the spinlock, and actually might allow to avoid one atomic
op in a number of cases.
3) Shrink the size of BufferDesc by removing buf_id; that'd bring it to
64byte.
I'm a bit hesitant to go for 3), because it'd likely end up adding a bit
of arithmetic to a number of places in bufmgr.c. Robert, what do you
think?
Andres
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