From mboxrd@z Thu Jan 1 00:00:00 1970 From: john cooper Subject: Resend: patch: qemu + hugetlbfs.. Date: Mon, 25 Aug 2008 19:05:17 -0400 Message-ID: <48B33AAD.8000508@third-harmonic.com> References: <4873E400.4000409@third-harmonic.com> <4873F395.6030209@codemonkey.ws> <4874051A.8000802@third-harmonic.com> <48740F86.3050306@codemonkey.ws> <20080709170301.GA11439@dmt.cnet> <4874F156.2010708@codemonkey.ws> <48763B86.6060402@third-harmonic.com> <48764DAF.6060502@codemonkey.ws> <48766E03.4090901@third-harmonic.com> <48767558.50301@codemonkey.ws> <48767B20.20806@third-harmonic.com> <4876815E.3010109@codemonkey.ws> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------070202070203060502040202" Cc: Anthony Liguori , Marcelo Tosatti , john.cooper@redhat.com, avi@qumranet.com To: kvm@vger.kernel.org Return-path: Received: from dpc691978010.direcpc.com ([69.19.78.10]:55137 "EHLO anvil.third-harmonic.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753796AbYHYXHx (ORCPT ); Mon, 25 Aug 2008 19:07:53 -0400 In-Reply-To: <4876815E.3010109@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------070202070203060502040202 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit This patch from over a month ago doesn't seem to have made it into kvm-73 and may have been lost in the shuffle. Attached is essentially the same patch but as applied to kvm-73, and validated relative to that version. In a nutshell the intention here is to allow preallocation of guest huge page backed memory at qemu initialization time to avoid a quirk in the kernel's huge page accounting allowing overcommit of huge pages. Failure of the kernel to resolve a guest fault to overcommitted huge page memory during runtime results in sigkill termination of the guest. This patch provides the option of avoiding such behavior at the cost of up-front preallocation of physical huge pages backing the guest. -john Anthony Liguori wrote: > john cooper wrote: >> Anthony Liguori wrote: >>> john cooper wrote: >>>> As it currently exists alloc_hpage_mem() is tied to >>>> the notion of huge page allocation as it will reference >>>> gethugepagesize() irrespective of *mem_path. So even >>>> in the case of tmpfs backed files, if the host kernel >>>> has been configured with CONFIG_HUGETLBFS we will wind >>>> up doing allocations of /dev/shm mapped files at >>>> /proc/meminfo:Hugepagesize granularity. >>> >>> Which is fine. It just means we round -m values up to even numbers. >> >> Well, yes it will round the allocation. But from a >> minimally sufficient 4KB boundary to that of 4MB/2MB >> relative to a 32/64 bit x86 host which is excessive. >> >>>> Probably not what was intended but probably not too >>>> much of a concern as "-mem-path /dev/shm" is likely >>>> only used in debug of this flag and associated logic. >>>> I don't see it currently being worth the trouble to >>>> correct from a squeaky clean POV, and doing so may >>>> drag in far more than the header file we've just >>>> booted above to deal with this architecture/config >>>> dependency. >>> >>> Renaming a function to a name that's less accurate seems bad to me. >>> I don't mean to be pedantic, but it seems like a strange thing to >>> do. I prefer it the way it was before. >> >> I don't see any harm reverting the name. But I do >> believe it is largely cosmetic as given the above, >> the current code does require some work to make it >> independent of huge page assumptions. Update attached. >> >> -john > > Looks good to me. > > Acked-by: Anthony Liguori > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- john.cooper@third-harmonic.com --------------070202070203060502040202 Content-Type: text/plain; name="prealloc.diff-080825" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="prealloc.diff-080825" vl.c | 48 ++++++++++++++++++++++++++++++------------------ 1 file changed, 30 insertions(+), 18 deletions(-) ================================================================= --- ./qemu/vl.c.PAORG +++ ./qemu/vl.c @@ -239,6 +239,7 @@ int autostart = 1; int time_drift_fix = 0; unsigned int kvm_shadow_memory = 0; const char *mem_path = NULL; +int mem_prealloc = 1; /* force preallocation of physical target memory */ int hpagesize = 0; const char *cpu_vendor_string; #ifdef TARGET_ARM @@ -8423,7 +8424,10 @@ static void help(int exitcode) #endif "-tdf inject timer interrupts that got lost\n" "-kvm-shadow-memory megs set the amount of shadow pages to be allocated\n" - "-mem-path set the path to hugetlbfs/tmpfs mounted directory, also enables allocation of guest memory with huge pages\n" + "-mem-path set the path to hugetlbfs/tmpfs mounted directory, also\n" + " enables allocation of guest memory with huge pages\n" + "-mem-prealloc toggles preallocation of -mem-path backed physical memory\n" + " at startup. Default is enabled.\n" "-option-rom rom load a file, rom, into the option ROM space\n" #ifdef TARGET_SPARC "-prom-env variable=value set OpenBIOS nvram variables\n" @@ -8546,6 +8550,7 @@ enum { QEMU_OPTION_tdf, QEMU_OPTION_kvm_shadow_memory, QEMU_OPTION_mempath, + QEMU_OPTION_mem_prealloc }; typedef struct QEMUOption { @@ -8671,6 +8676,7 @@ const QEMUOption qemu_options[] = { { "tb-size", HAS_ARG, QEMU_OPTION_tb_size }, { "icount", HAS_ARG, QEMU_OPTION_icount }, { "mem-path", HAS_ARG, QEMU_OPTION_mempath }, + { "mem-prealloc", 0, QEMU_OPTION_mem_prealloc }, { NULL }, }; @@ -8890,11 +8896,13 @@ static int gethugepagesize(void) return hugepagesize; } +/* attempt to allocate memory mmap'ed to mem_path + */ void *alloc_mem_area(unsigned long memory, const char *path) { char *filename; void *area; - int fd; + int fd, flags; if (asprintf(&filename, "%s/kvm.XXXXXX", path) == -1) return NULL; @@ -8922,26 +8930,27 @@ void *alloc_mem_area(unsigned long memor */ ftruncate(fd, memory); - area = mmap(0, memory, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0); - if (area == MAP_FAILED) { - perror("mmap"); - close(fd); - return NULL; - } - - return area; + /* NB: MAP_POPULATE won't exhaustively alloc all phys pages in the case + * MAP_PRIVATE is requested. For mem_prealloc we mmap as MAP_SHARED + * to sidestep this quirk. + */ + flags = mem_prealloc ? MAP_POPULATE|MAP_SHARED : MAP_PRIVATE; + area = mmap(0, memory, PROT_READ|PROT_WRITE, flags, fd, 0); + if (area != MAP_FAILED) + return (area); + perror("alloc_mem_area: can't mmap hugetlbfs pages"); + close(fd); + return (NULL); } -void *qemu_alloc_physram(unsigned long memory) +/* allocate guest memory as requested + */ +void *qemu_alloc_physram(unsigned long size) { - void *area = NULL; - if (mem_path) - area = alloc_mem_area(memory, mem_path); - if (!area) - area = qemu_vmalloc(memory); - - return area; + return (alloc_mem_area(size, mem_path)); + else + return (qemu_vmalloc(size)); } int main(int argc, char **argv) @@ -9546,6 +9555,9 @@ int main(int argc, char **argv) case QEMU_OPTION_mempath: mem_path = optarg; break; + case QEMU_OPTION_mem_prealloc: + mem_prealloc = !mem_prealloc; + break; case QEMU_OPTION_name: qemu_name = optarg; break; --------------070202070203060502040202--