Date: Fri, 8 Oct 2021 09:25:27 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 174aad047e12 - main - vm_fault: do not trigger OOM too early Message-ID: <202110080925.1989PRgf066947@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=174aad047e12e8f30f9a5919ca1c08919441a217 commit 174aad047e12e8f30f9a5919ca1c08919441a217 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-10-04 06:36:02 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2021-10-08 09:24:46 +0000 vm_fault: do not trigger OOM too early Wakeup in vm_waitpfault() does not mean that the thread would get the page on the next vm_page_alloc() call, other thread might steal the free page we were waiting for. On the other hand, this wakeup might come much earlier than just vm_pfault_oom_wait seconds, if the rate of the page reclamation is high enough. If wakeups come fast and we loose the allocation race enough times, OOM could be undeservably triggered much earlier than vm_pfault_oom_attempts x vm_pfault_oom_wait seconds. Fix it by not counting the number of sleeps, but measuring the time to th first allocation failure, and triggering OOM when it was older than oom_attempts x oom_wait seconds. Reviewed by: markj Tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 2 weeks Differential revision: https://reviews.freebsd.org/D32287 --- sys/vm/vm_fault.c | 52 +++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 37 insertions(+), 15 deletions(-) diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index 5cfe7d1ae315..8a4b5a543dd6 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -125,7 +125,8 @@ struct faultstate { vm_prot_t fault_type; vm_prot_t prot; int fault_flags; - int oom; + struct timeval oom_start_time; + bool oom_started; boolean_t wired; /* Page reference for cow. */ @@ -1073,6 +1074,38 @@ vm_fault_zerofill(struct faultstate *fs) vm_page_valid(fs->m); } +/* + * Initiate page fault after timeout. Returns true if caller should + * do vm_waitpfault() after the call. + */ +static bool +vm_fault_allocate_oom(struct faultstate *fs) +{ + struct timeval now; + + unlock_and_deallocate(fs); + if (vm_pfault_oom_attempts < 0) + return (true); + if (!fs->oom_started) { + fs->oom_started = true; + getmicrotime(&fs->oom_start_time); + return (true); + } + + getmicrotime(&now); + timevalsub(&now, &fs->oom_start_time); + if (now.tv_sec < vm_pfault_oom_attempts * vm_pfault_oom_wait) + return (true); + + if (bootverbose) + printf( + "proc %d (%s) failed to alloc page on fault, starting OOM\n", + curproc->p_pid, curproc->p_comm); + vm_pageout_oom(VM_OOM_MEM_PF); + fs->oom_started = false; + return (false); +} + /* * Allocate a page directly or via the object populate method. */ @@ -1136,22 +1169,11 @@ vm_fault_allocate(struct faultstate *fs) fs->m = vm_page_alloc(fs->object, fs->pindex, alloc_req); } if (fs->m == NULL) { - unlock_and_deallocate(fs); - if (vm_pfault_oom_attempts < 0 || - fs->oom < vm_pfault_oom_attempts) { - fs->oom++; + if (vm_fault_allocate_oom(fs)) vm_waitpfault(dset, vm_pfault_oom_wait * hz); - } else { - if (bootverbose) - printf( - "proc %d (%s) failed to alloc page on fault, starting OOM\n", - curproc->p_pid, curproc->p_comm); - vm_pageout_oom(VM_OOM_MEM_PF); - fs->oom = 0; - } return (KERN_RESOURCE_SHORTAGE); } - fs->oom = 0; + fs->oom_started = false; return (KERN_NOT_RECEIVER); } @@ -1300,7 +1322,7 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type, fs.fault_flags = fault_flags; fs.map = map; fs.lookup_still_valid = false; - fs.oom = 0; + fs.oom_started = false; faultcount = 0; nera = -1; hardfault = false;
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