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 m4XFBOks 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000294, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 24, 2024 at 01:51:11PM GMT, Pedro Falcato wrote: > On Tue, Sep 24, 2024 at 12:16:27PM GMT, Lorenzo Stoakes wrote: > > process_madvise() was conceived as a useful means for performing a vector > > of madvise() operations on a remote process's address space. > > > > However it's useful to be able to do so on the current process also. It is > > currently rather clunky to do this (requiring a pidfd to be opened for the > > current process) and introduces unnecessary overhead in incrementing > > reference counts for the task and mm. > > > > Avoid all of this by providing a PR_MADV_SELF flag, which causes > > process_madvise() to simply ignore the pidfd parameter and instead apply > > the operation to the current process. > > > > How about simply defining a pseudo-fd PIDFD_SELF in the negative int space? > There's precedent for it in the fs space (AT_FDCWD). I think it's more ergonomic > and if you take out the errno space we have around 2^31 - 4096 available sentinel > values. > > e.g: > > /* AT_FDCWD = -10, -1 is dangerous, pick a different value */ > #define PIDFD_SELF -11 > > int pidfd = target_pid == getpid() ? PIDFD_SELF : pidfd_open(...); > process_madvise(pidfd, ...); > > > What do you think? I like the way you're thinking, but I don't think this is something we can do in the context of this series. I mean, I totally accept using a flag here and ignoring the pidfd field is _ugly_, no question. But I'm trying to find the smallest change that achieves what we want. To add such a sentinel would be a change to the pidfd mechanism as a whole, and we'd be left in the awkward situation that no other user of the pidfd mechanism would be implementing this, but we'd have to expose this as a general sentinel value for all pidfd users. One nice thing with doing this as a flag is that, later, if somebody is willing to do the larger task of having a special sentinel pidfd value to mean 'the current process', we could use this in process_madvise() and deprecate this flag :) > > -- > Pedro