At Mon, 05 Nov 2012 16:06:26 +0800,
Liu Yuan wrote:
> >> +static int zero_out_jfile(int fd)
> >> +{
> >> + char *buf;
> >> + ssize_t wlen;
> >> +
> >> + buf = valloc(JOURNAL_FILE_SIZE);
> >> + memset(buf, 0, JOURNAL_FILE_SIZE);
> >> + wlen = xpwrite(fd, buf, JOURNAL_FILE_SIZE, 0);
> >
> > Isn't it efficent to use truncate and fallocate like as follows?
> >
> > ftruncate(fd, 0);
> > prealloc(fd, JOURNAL_FILE_SIZE);
> >
> >
>
> fallocate will allocate physical blocks but the extents of those blocks
> is marked as 'unwritten'. So the some writes will be delayed slightly to
> change those 'unwritten' extents into 'written' ones of meta data.
Okay, makes sense.
Thanks,
Kazutaka
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