On Thu, Oct 17, 2024 at 12:51:04AM +0000, jeffxu@xxxxxxxxxxxx wrote: > From: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > Two fixes for madvise(MADV_DONTNEED) when sealed. > Please separate these fixes into two separate patches. > For PROT_NONE mappings, the previous blocking of > madvise(MADV_DONTNEED) is unnecessary. As PROT_NONE already prohibits > memory access, madvise(MADV_DONTNEED) should be allowed to proceed in > order to free the page. I don't get it. Is there an actual use case for this? > For file-backed, private, read-only memory mappings, we previously did > not block the madvise(MADV_DONTNEED). This was based on > the assumption that the memory's content, being file-backed, could be > retrieved from the file if accessed again. However, this assumption > failed to consider scenarios where a mapping is initially created as > read-write, modified, and subsequently changed to read-only. The newly > introduced VM_WASWRITE flag addresses this oversight. We *do not* need this. It's sufficient to just block discard operations on read-only private mappings. Sending a possible (fully untested) fix. If you like this approach I can resend properly, or Andrew can pick it up, whatever floats people's boats. ----8<----
