On Mon, Oct 8, 2018 at 12:20 PM Cameron Simpson <[email protected]> wrote: > > On 08Oct2018 10:56, Ram Rachum <[email protected]> wrote: > >That's incredibly interesting. I've never used mmap before. > >However, there's a problem. > >I did a few experiments with mmap now, this is the latest: > > > >path = pathlib.Path(r'P:\huge_file') > > > >with path.open('r') as file: > > mmap = mmap.mmap(file.fileno(), 0, access=mmap.ACCESS_READ) > > Just a remark: don't tromp on the "mmap" name. Maybe "mapped"? > > > for match in re.finditer(b'.', mmap): > > pass > > > >The file is 338GB in size, and it seems that Python is trying to load it > >into memory. The process is now taking 4GB RAM and it's growing. I saw the > >same behavior when searching for a non-existing match. > > > >Should I open a Python bug for this? > > Probably not. First figure out what is going on. BTW, how much RAM have you > got? > > As you access the mapped file the OS will try to keep it in memory in case you > need that again. In the absense of competition, most stuff will get paged out > to accomodate it. That's normal. All the data are "clean" (unmodified) so the > OS can simply release the older pages instantly if something else needs the > RAM. > > However, another possibility is the the regexp is consuming lots of memory. > > The regexp seems simple enough (b'.'), so I doubt it is leaking memory like > mad; I'm guessing you're just seeing the OS page in as much of the file as it > can.
Yup. Windows will aggressively fill up your RAM in cases like this because after all why not? There's no use to having memory just sitting around unused. For read-only, non-anonymous mappings it's not much problem for the OS to drop pages that haven't been recently accessed and use them for something else. So I wouldn't be too worried about the process chewing up RAM. I feel like this is veering more into python-list territory for further discussion though. _______________________________________________ Python-ideas mailing list [email protected] https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
