Date: Thu, 15 Nov 2012 12:31:55 -0600 From: Alan Cox <alc@rice.edu> To: Konstantin Belousov <kostikbel@gmail.com> Cc: alc@freebsd.org, pho@freebsd.org, Sushanth Rai <sushanth_rai@yahoo.com>, StevenSears <Steven.Sears@netapp.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: Memory reserves or lack thereof Message-ID: <50A5351B.3030108@rice.edu> In-Reply-To: <20121115182153.GF73505@kib.kiev.ua> References: <20121112133638.GZ73505@kib.kiev.ua> <1352755682.93266.YahooMailClassic@web181701.mail.ne1.yahoo.com> <20121112214808.GH73505@kib.kiev.ua> <50A181C9.7030209@rice.edu> <20121113115445.GK73505@kib.kiev.ua> <50A52722.7050100@rice.edu> <20121115182153.GF73505@kib.kiev.ua>
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On 11/15/2012 12:21, Konstantin Belousov wrote: > On Thu, Nov 15, 2012 at 11:32:18AM -0600, Alan Cox wrote: >> On 11/13/2012 05:54, Konstantin Belousov wrote: >>> On Mon, Nov 12, 2012 at 05:10:01PM -0600, Alan Cox wrote: >>>> On 11/12/2012 3:48 PM, Konstantin Belousov wrote: >>>>> On Mon, Nov 12, 2012 at 01:28:02PM -0800, Sushanth Rai wrote: >>>>>> This patch still doesn't address the issue of M_NOWAIT calls driving >>>>>> the memory the all the way down to 2 pages, right ? It would be nice to >>>>>> have M_NOWAIT just do non-sleep version of M_WAITOK and M_USE_RESERVE >>>>>> flag to dig deep. >>>>> This is out of scope of the change. But it is required for any further >>>>> adjustements. >>>> I would suggest a somewhat different response: >>>> >>>> The patch does make M_NOWAIT into a "non-sleep version of M_WAITOK" and >>>> does reintroduce M_USE_RESERVE as a way to specify "dig deep". >>>> >>>> Currently, both M_NOWAIT and M_WAITOK can drive the cache/free memory >>>> down to two pages. The effect of the patch is to stop M_NOWAIT at two >>>> pages rather than allowing it to continue to zero pages. >>>> >>>> When you say, "This is out of scope ...", I believe that you are >>>> referring to changing two pages into something larger. I agree that >>>> this is out of scope for the current change. >>> I referred exactly to the difference between M_USE_RESERVE set or not. >>> IMO this is what was asked by the question author. So yes, my mean of >>> the 'out of scope' is about tweaking the 'two pages reserve' in some >>> way. >> Since M_USE_RESERVE is no longer deprecated in HEAD, here is my proposed >> man page update to malloc(9): >> >> Index: share/man/man9/malloc.9 >> =================================================================== >> --- share/man/man9/malloc.9 (revision 243091) >> +++ share/man/man9/malloc.9 (working copy) >> @@ -29,7 +29,7 @@ >> .\" $NetBSD: malloc.9,v 1.3 1996/11/11 00:05:11 lukem Exp $ >> .\" $FreeBSD$ >> .\" >> -.Dd January 28, 2012 >> +.Dd November 15, 2012 >> .Dt MALLOC 9 >> .Os >> .Sh NAME >> @@ -153,13 +153,12 @@ if >> .Dv M_WAITOK >> is specified. >> .It Dv M_USE_RESERVE >> -Indicates that the system can dig into its reserve in order to obtain the >> -requested memory. >> -This option used to be called >> -.Dv M_KERNEL >> -but has been renamed to something more obvious. >> -This option has been deprecated and is slowly being removed from the >> kernel, >> -and so should not be used with any new programming. >> +Indicates that the system can use its reserve of memory to satisfy the >> +request. >> +This option should only be used in combination with >> +.Dv M_NOWAIT >> +when an allocation failure cannot be tolerated by the caller without >> +catastrophic effects on the system. >> .El >> .Pp >> Exactly one of either > The text looks fine. Shouldn't the requirement for M_USE_RESERVE be also > expressed in KASSERT, like this: > > diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h > index d9e4692..f8a4f70 100644 > --- a/sys/vm/vm_page.h > +++ b/sys/vm/vm_page.h > @@ -353,6 +351,9 @@ malloc2vm_flags(int malloc_flags) > { > int pflags; > > + KASSERT((malloc_flags & M_USE_RESERVE) == 0 || > + (malloc_flags & M_NOWAIT) != 0, > + ("M_USE_RESERVE requires M_NOWAIT")); > pflags = (malloc_flags & M_USE_RESERVE) != 0 ? VM_ALLOC_INTERRUPT : > VM_ALLOC_SYSTEM; > if ((malloc_flags & M_ZERO) != 0) > > I understand that this could be added to places of the allocator's entries, > but I think that the page allocations are fine too. Yes, please do that. Alan
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