Date: Fri, 11 Oct 2002 06:01:55 -0700 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Peter Wemm <peter@wemm.org>, Sean Kelly <smkelly@zombie.org>, hackers@FreeBSD.ORG Subject: Re: swapoff? Message-ID: <20021011130154.GA16549@HAL9000.homeunix.com> In-Reply-To: <200210081745.g98Hjkam078883@apollo.backplane.com> References: <20020713071911.GA1558@HAL9000.wox.org> <20020713073404.9869A3811@overcee.wemm.org> <20020713115746.GA2162@HAL9000.wox.org> <200207131636.g6DGaoqh081285@apollo.backplane.com> <20021007153845.GA371@HAL9000.homeunix.com> <200210072347.g97Nl3Zo049415@apollo.backplane.com> <20021008113614.GA319@HAL9000.homeunix.com> <200210081745.g98Hjkam078883@apollo.backplane.com>
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Thus spake Matthew Dillon <dillon@apollo.backplane.com>:
> This is a sticky situation because both the VM object and the
> swblocks may be manipulated by other processes when you block. I
> think what you need to try to do is this (it's a mess, if you can think
> of a better solution definitely go another route!)
>
> while ((swap = *pswap) != NULL) {
> if (anything_is_swapped_to_the_device) {
> try_to_page_it_all_in
> (note that the swblock structure is invalid the moment you
> block, so swp_pager_force_pagein() should be given
> the whole range).
> /* fall through to retry */
> } else if (the_related_object_pip_count_is_not_zero) {
> vm_object_pip_sleep(...)
> /* fall through to retry */
> } else if (swap->swb_count <= 0) {
> free the swap block
> *pswap = swap->swb_hnext;
> }
> }
Thanks, your solution looks pretty good. I guess as part of the
try_to_page_it_all_in, I'll want to call swap_pager_unswapped() on
each page. Now I really wish I had noticed swap_pager_unswapped()
earlier; it would have made my job much easier!
I'm worried that vm_proc_swapin_all() has a similar race with the
swapout daemon. Presently I assume that my references to the
UPAGES object and the associated pages remain valid after the
faultin(), and that I can use swap_pager_freeswapspace() to free
the correct metadata, instead of calling swap_pager_unswapped() on
each page. Should just hold the process lock until the metadata
are freed?
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