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    SubjectRe: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM


    On Mon, 23 Apr 2018, Michal Hocko wrote:

    > On Mon 23-04-18 10:06:08, Mikulas Patocka wrote:
    >
    > > > > He didn't want to fix vmalloc(GFP_NOIO)
    > > >
    > > > I don't remember that conversation, so I don't know whether I agree with
    > > > his reasoning or not. But we are supposed to be moving away from GFP_NOIO
    > > > towards marking regions with memalloc_noio_save() / restore. If you do
    > > > that, you won't need vmalloc(GFP_NOIO).
    > >
    > > He said the same thing a year ago. And there was small progress. 6 out of
    > > 27 __vmalloc calls were converted to memalloc_noio_save in a year - 5 in
    > > infiniband and 1 in btrfs. (the whole discussion is here
    > > http://lkml.iu.edu/hypermail/linux/kernel/1706.3/04681.html )
    >
    > Well this is not that easy. It requires a cooperation from maintainers.
    > I can only do as much. I've posted patches in the past and actively
    > bringing up this topic at LSFMM last two years...

    You're right - but you have chosen the uneasy path. Fixing __vmalloc code
    is easy and it doesn't require cooperation with maintainers.

    > > He refuses 15-line patch to fix GFP_NOIO bug because he believes that in 4
    > > years, the kernel will be refactored and GFP_NOIO will be eliminated. Why
    > > does he have veto over this part of the code? I'd much rather argue with
    > > people who have constructive comments about fixing bugs than with him.
    >
    > I didn't NACK the patch AFAIR. I've said it is not a good idea longterm.
    > I would be much more willing to change my mind if you would back your
    > patch by a real bug report. Hacks are acceptable when we have a real
    > issue in hands. But if we want to fix potential issue then better make
    > it properly.

    Developers should fix bugs in advance, not to wait until a crash hapens,
    is analyzed and reported.

    What's the problem with 15-line hack? Is the problem that kernel
    developers would feel depressed when looking the source code? Other than
    harming developers' feelings, I don't see what kind of damange could that
    piece of code do.

    Mikulas

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