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vm_fault: do not trigger OOM too early

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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
This commit is contained in:
Konstantin Belousov 2021-10-04 09:36:02 +03:00
parent 7e64580b5f
commit 174aad047e
1 changed files with 37 additions and 15 deletions
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52
sys/vm/vm_fault.c
View File

@ -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;