On Tue, Jan 14, 2025 at 10:50:01AM +0100, Alice Ryhl wrote: > On Mon, Jan 13, 2025 at 3:45 PM Lorenzo Stoakes > <lorenzo.stoakes@xxxxxxxxxx> wrote: > > > >> > For a series at v11 where there is broad agreement with maintainers within > > > >> > the subsystem which it wraps, perhaps the priority should be to try to have > > > >> > the series merged unless there is significant technical objection from the > > > >> > rust side? > > > >> > > > > >> >> > > > >> >> How about this: > > > >> >> > > > >> >> This clears the virtual memory map for the range given by `start` and > > > >> >> `size`, dropping refcounts to memory held by the mappings in this range. That > > > >> >> is, anonymous memory is completely freed, file-backed memory has its > > > >> >> reference count on page cache folio's dropped, any dirty data will still > > > >> >> be written back to disk as usual. > > > >> > > > > >> > Sorry I object to this, 'clears the virtual memory map' is really > > > >> > vague. What is already there is better. > > > >> > > > >> Would you like the proposed paragraph if we replaced "virtual memory > > > >> map" with "page table mappings", or do you object to the entirety of the > > > >> new suggestion? > > > > > > > > I object to the suggestion in general. The description is fine as it is. > > > > > > Ok. I'm raising a flag because I had more questions after reading the > > > docstring than before. > > > > Sure and so I think this is valuable information, and indicates it's > > probably worthwhile adding a little extra information on mentioning page > > tables. > > Sorry, I'm a bit lost. What would you like me to add? Perhaps there's > an existing file in Documentation/ that I can link to? Sure no problem, I propose expanding: /// This clears page table mappings for the range at the leaf level, leaving all other page /// tables intact, /// anonymous memory is completely freed, file-backed memory has its reference count on page /// cache folio's dropped, any dirty data will still be written back to disk as usual. To include information on page tables. I suggest something like: /// It may seem odd that we clear at the leaf level, this is however a product /// of the page table structure used to map physical memory into a virtual /// address space - each virtual address actually consists of a bitmap of array /// indices into page tables, which form a hierarchical page table level /// structure. /// /// As a result, each page table level maps a multiple of page table levels /// below, and thus span ever increasing ranges of pages. At the leaf or PTE /// level, we map the actual physical memory. /// /// It is here where a zap operates, as it the only place we can be certain of /// clearing without impacting any other virtual mappings. It is an /// implementation detail as to whether the kernel goes further in freeing /// unused page tables, but for the purposes of this operation we must only /// assume that the leaf level is cleared. Alice, Andreas - please let me know if this makes sense/is clear or needs further clarification. > > Alice
