On Tue 03-09-19 05:22:08, Matthew Wilcox wrote: > On Tue, Sep 03, 2019 at 02:14:24PM +0200, Michal Hocko wrote: > > On Mon 02-09-19 03:23:41, William Kucharski wrote: > > > Add filemap_huge_fault() to attempt to satisfy page > > > faults on memory-mapped read-only text pages using THP when possible. > > > > This deserves much more description of how the thing is implemented and > > expected to work. For one thing it is not really clear to me why you > > need CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP at all. You need a support > > from the filesystem anyway. So who is going to enable/disable this > > config? > > There are definitely situations in which enabling this code will crash > the kernel. But we want to get filesystems to a point where they can > start working on their support for large pages. So our workaround is > to try to get the core pieces merged under a CONFIG_I_KNOW_WHAT_IM_DOING > flag and let people play with it. Then continue to work on the core > to eliminate those places that are broken. I am not sure I understand. Each fs has to opt in to the feature anyway. If it doesn't then there should be no risk of regression, right? I do not expect any fs would rush an implementation in while not being sure about the correctness. So how exactly does a config option help here. > > I cannot really comment on fs specific parts but filemap_huge_fault > > sounds convoluted so much I cannot wrap my head around it. One thing > > stand out though. The generic filemap_huge_fault depends on ->readpage > > doing the right thing which sounds quite questionable to me. If nothing > > else I would expect ->readpages to do the job. > > Ah, that's because you're not a filesystem person ;-) ->readpages is > really ->readahead. It's a crappy interface and should be completely > redesigned. OK, the interface looked like the right fit for this purpose. Thanks for clarifying. -- Michal Hocko SUSE Labs
