On Tue, Apr 25, 2023 at 12:16 PM Andres Freund <andres@anarazel.de> wrote:
> On 2023-04-24 15:32:25 -0700, Andres Freund wrote:
> > We obviously can add a retry loop to FileFallocate(), similar to what's
> > already present e.g. in FileRead(). But I wonder if we shouldn't go a bit
> > further, and do it for all the fd.c routines where it's remotely plausible
> > EINTR could be returned? It's a bit silly to add EINTR retries one-by-one to
> > the functions.
> >
> >
> > The following are documented to potentially return EINTR, without fd.c having
> > code to retry:
> >
> > - FileWriteback() / pg_flush_data()
> > - FileSync() / pg_fsync()
> > - FileFallocate()
> > - FileTruncate()
> >
> > With the first two there's the added complication that it's not entirely
> > obvious whether it'd be better to handle this in File* or pg_*. I'd argue the
> > latter is a bit more sensible?
>
> A prototype of that approach is attached. I pushed the retry handling into the
> pg_* routines where applicable. I guess we could add pg_* routines for
> FileFallocate(), FilePrewarm() etc as well, but I didn't do that here.
One problem we ran into with the the shm_open() case (which is nearly
identical under the covers, since shm_open() just opens a file in a
tmpfs on Linux) was that a simple retry loop like this could never
terminate if the process was receiving a lot of signals from the
recovery process, which is why we went with the idea of masking
signals instead. Eventually we should probably grow the file in
smaller chunks with a CFI in between so that we both guarantee that we
make progress (by masking for smaller size increases) and service
interrupts in a timely fashion (by unmasking between loops). I don't
think that applies here because we're not trying to fallocate
humongous size increases in one go, but I just want to note that we're
making a different choice. I think this looks reasonable for the use
cases we actually have here.
