Date: Thu, 19 Sep 2019 09:12:16 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Yoshihiro Ota <ota@j.email.ne.jp> Cc: freebsd-hackers@freebsd.org Subject: Re: How to access user process memory/pages from swap_pager.c Message-ID: <20190919061216.GG2559@kib.kiev.ua> In-Reply-To: <20190919003419.007b6de7f9887617f254e334@j.email.ne.jp> References: <20190919003419.007b6de7f9887617f254e334@j.email.ne.jp>
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On Thu, Sep 19, 2019 at 12:34:19AM -0400, Yoshihiro Ota wrote: > Hi, > > I'm trying to get some data / statistics for pages being swapped out. > > I'm trying to access pages being swapped out in swp_pager_putpages. > Given I have access to vm_page_t, it looked like I would be able to use VM_PAGE_TO_PHYS() to access user pages. > > However, I get page-fault panics like: > panic: vm_fault_hold: fault on nofault entry, addr: 0 > > Which functions/setup do I need to access/copy user data being swapped? I am not sure what you are trying to do, but whatever is it, it is unreasonable. When a page is swapped out, its physical memory frame, described by vm_page_t, is reused for something else. The only resource consumed by swapped out page is the index in the vm_object page queue, swap space which holds the actual content, and pointer from swap pager data to the swap location.
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