On Tue, Jan 14, 2025 at 12:57 PM Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> wrote: > > 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. That looks reasonable to me. Thanks! Do you have thoughts on the wordings I proposed here? https://lore.kernel.org/all/CAH5fLginc=uNPVp1-T-oBrgtE1oi_cBMd65sPkDgqSDjH_CNfA@xxxxxxxxxxxxxx/ Alice
