On Thu, Dec 12, 2024 at 09:46:03PM +1300, Barry Song wrote: > On Thu, Dec 12, 2024 at 9:29 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > On Thu, Dec 12, 2024 at 08:37:11PM +1300, Barry Song wrote: > > > From: Barry Song <v-songbaohua@xxxxxxxx> > > > > > > While developing the zeromap series, Usama observed that certain > > > workloads may contain over 10% zero-filled pages. This may present > > > an opportunity to save memory by mapping zero-filled pages to zero_pfn > > > in do_swap_page(). If a write occurs later, do_wp_page() can > > > allocate a new page using the Copy-on-Write mechanism. > > > > Shouldn't this be done during, or rather instead of swap out instead? > > Swapping all zero pages out just to optimize the in-memory > > representation on seems rather backwards. > > I’m having trouble understanding your point—it seems like you might > not have fully read the code. :-) I've not read the code at all, I've read your commit log. > The situation is as follows: for a zero-filled page, we are currently > allocating a new > page unconditionally. By mapping this zero-filled page to zero_pfn, we could > save the memory used by this page. Yes. But why do that in swap-in and not swap-out?
