On Thu, Feb 22, 2018 at 09:27:41AM -0800, Darrick J. Wong wrote:
> On Thu, Feb 22, 2018 at 04:06:14PM +0000, Luis Henriques wrote:
> > On Thu, Dec 14, 2017 at 06:07:31PM -0800, Darrick J. Wong wrote:
> >
> > <snip>
> >
> > > +void
> > > +clonerange_f(
> > > + int opno,
> > > + long r)
> > > +{
> >
> > <snip>
> >
> > > + /* Calculate offsets */
> > > + len = (random() % FILELEN_MAX) + 1;
> > > + len &= ~(stat1.st_blksize - 1);
> > > + if (len == 0)
> > > + len = stat1.st_blksize;
> > > + if (len > stat1.st_size)
> > > + len = stat1.st_size;
> > > +
> > > + lr = ((__int64_t)random() << 32) + random();
> > > + if (stat1.st_size == len)
> > > + off1 = 0;
> > > + else
> > > + off1 = (off64_t)(lr % MIN(stat1.st_size - len, MAXFSIZE));
> > > + off1 %= maxfsize;
> > > + off1 &= ~(stat1.st_blksize - 1);
> > > +
> > > + /*
> > > + * If srcfile == destfile, randomly generate destination ranges
> > > + * until we find one that doesn't overlap the source range.
> > > + */
> > > + do {
> > > + lr = ((__int64_t)random() << 32) + random();
> > > + off2 = (off64_t)(lr % MIN(stat2.st_size + (1024 * 1024), MAXFSIZE));
> > > + off2 %= maxfsize;
> > > + off2 &= ~(stat2.st_blksize - 1);
> > > + } while (stat1.st_ino == stat2.st_ino && llabs(off2 - off1) < len);
> >
> > I started seeing hangs in generic/013 on cephfs. After spending some
> > time looking, I found that this loops forever. And the reason seems to
> > be that stat1.st_blksize is too big for this filesystem (4M) -- when
> > doing:
>
> "Too big for this filesystem"?
>
> Uh... maybe you'd better start by giving me more stat buffer info --
> what's st_size?
>
> > off1 &= ~(stat1.st_blksize - 1);
>
> These bits round the start offset down to block granularity, since clone
> range implementations generally require that the ranges align to block
> boundaries.
>
> (Though AFAICT ceph doesn't support clone range anyway...)
>
> So reading between the lines, is the problem here that ceph advertises a
> blocksize of 4M and fsstress calls clonerange_f with files that are
> smaller than 4M in size, so the only possible offsets with a 4M
> blocksize are zero and that's why we end up looping forever?
Brilliantly described! That is *exactly* what I'm seeing and failed to
describe. I guess I could use FSSTRESS_AVOID to work around this issue,
but there are probably better options.
Cheers,
--
Luís
>
> --D
>
> >
> > off1 (and off2) will both end up with 0. Does this make sense? Would
> > something like:
> >
> > - off1 &= ~(stat1.st_blksize - 1);
> > + if (stat1.st_blksize <= stat1.st_size)
> > + off1 &= ~(stat1.st_blksize - 1);
> >
> > be acceptable? (and a similar change for off2, of course.)
>
> > Cheers,
> > --
> > Luís
> > --
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