At Wed, 26 Apr 2023 11:37:55 +1200, Thomas Munro <thomas.mu...@gmail.com> wrote in > On Tue, Apr 25, 2023 at 12:16 PM Andres Freund <and...@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.
FWIW I share the same feeling about looping by EINTR without signals being blocked. If we just retry the same operation without processing signals after getting EINTR, I think blocking signals is better. We could block signals more gracefully, but I'm not sure it's worth the complexity. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
