On Thu, Sep 17, 2020 at 10:00 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Sep 17, 2020 at 12:27 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > Ah, I see what you mean. Hold the i_mmap_rwsem for write across, > > basically, the entirety of truncate_inode_pages_range(). > > I really suspect that will be entirely unacceptable for latency > reasons, but who knows. In practice, nobody actually truncates a file > _while_ it's mapped, that's just crazy talk. > > But almost every time I go "nobody actually does this", I tend to be > surprised by just how crazy some loads are, and it turns out that > _somebody_ does it, and has a really good reason for doing odd things, > and has been doing it for years because it worked really well and > solved some odd problem. > > So the "hold it for the entirety of truncate_inode_pages_range()" > thing seems to be a really simple approach, and nice and clean, but it > makes me go "*somebody* is going to do bad things and complain about > page fault latencies". > Hi, I followed this thread a bit and see there is now a... commit 5ef64cc8987a9211d3f3667331ba3411a94ddc79 "mm: allow a controlled amount of unfairness in the page lock" By first reading I saw... + * (a) no special bits set: ... + * (b) WQ_FLAG_EXCLUSIVE: ... + * (b) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM: The last one should be (c). There was a second typo I cannot remember when you sent your patch without a commit message. Will look again. Thanks and Greetings, - Sedat -
