Hi, I'm sorry to reply so late because I was so busy with my job matters recently. I appreciate David's idea of simplifying the implement of tracking KSM-placed zero pages. But I'm confused with how to implement that via pte_mkdirty/pte_dirty without affecting other functions now and in the future. > >I already shared some feedback in [1]. I think we should try to simplify >this handling, as proposed in that mail. Still waiting for a reply. > >[1] >https://lore.kernel.org/all/9d7a8be3-ee9e-3492-841b-a0af9952ef36@xxxxxxxxxx/ I have some questions about using pte_mkdirty to mark KSM-placed zero pages. (1) Will KSM using pte_mkdirty to mark KSM-placed zero pages collides with the existing handling of the same pte in other featutes? And in the future, what if there are new codes also using pte_mkdirty for other goals. (2) Can the literal meaning of pte_mkdiry represents a pte that points to ksm zero page? (3) Suppose we use the pte_mkdirty approach, how to update/decline the count of ksm_zero_pages when upper app writting on the page triggers COW(Copy on Write)? In *mm_fault outside mm/ksm.c ? Move the previos message here to reply together. >The problem with this approach I see is that it fundamentally relies on >the rmap/stable-tree to detect whether a zeropage was placed or not. > >I was wondering, why we even need an rmap item *at all* anymore. Why >can't we place the shared zeropage an call it a day (remove the rmap >item)? Once we placed a shared zeropage, the next KSM scan should better >just ignore it, it's already deduplicated. The reason is as follows ... Initially, all scanned pages by ksmd will be assigned a rmap_item storing the page information and ksm information, which helps ksmd can know every scanned pages' status and update all counts especialy when COW happens. But since use_zero_pages feature was merged, the situation changed, ksm zero pages is the only exception of ksm-scanned page without owning a rmap_item in KSM, which leads to ksmd even don't know the existing of KSM-placed, and thus causes the problem of our patches aimed to solve.
