>> On 29.09.22 12:42, Claudio Imbrenda wrote: >> > On Thu, 29 Sep 2022 02:52:06 +0000 >> > xu.xin.sc@xxxxxxxxx wrote: >> > >> >> From: xu xin <xu.xin16@xxxxxxxxxx> >> >> >> >> Before enabling use_zero_pages by setting /sys/kernel/mm/ksm/ >> >> use_zero_pages to 1, pages_sharing of KSM is basically accurate. But >> >> after enabling use_zero_pages, all empty pages that are merged with >> >> kernel zero page are not counted in pages_sharing or pages_shared. >> > >> > that's because those pages are not shared between different processes. >> >> They are probably the most shared pages between processes in the kernel. > >shared from the kernel, though, not from other processes (that's what I >meant) > >> They are simply not KSM pages, that's what makes accounting tricky here. > >exactly. and those pages get shared all the time even without KSM, so >why care about those now? > >does it make a difference why a page is a zero page? WI's necessary to show these sharing zeros pages. Because: 1) Turning on/off use_zero_pages shouldn't make it so not transparent with the sharing zero pages. When administrators enable KSM and turn on use_zero_pages, if much memory increases due to zero pages sharing but they don't know the reasons compared to turning off use_zero_pages, isn't it confusing? 2) If no need to let users know how many full-zero-filled pages are merged by KSM due to use_zero_pages, then also no need to show pages_sharing and pages_shared to users. Besides, the description of pages_sharing in Documentation is wrong and MISLEADING when enabling use_zero_pages. 3) As David supposes, it also help for estimating memory demands when each and every shared page could get unshared. > >> >> > >> >> That is because the rmap_items of these ksm zero pages are not >> >> appended to The Stable Tree of KSM. >> >> >> >> We need to add the count of empty pages to let users know how many empty >> >> pages are merged with kernel zero page(s). >> > >> > why? >> > >> > do you need to know how many untouched zero pages a process has? >> > >> > does it make a difference if the zero page is really untouched or if it >> > was touched in the past but it is now zero? >> >> I'd also like to understand the rationale. Is it about estimating memory >> demands when each and every shared page could get unshared? >> >
