Add a VM flag to prevent reclaim on a failed contig allocation
If a M_WAITOK contig alloc fails, the VM subsystem will try to reclaim contiguous memory twice before actually failing the request. On a system with 64GB of RAM I've observed this take 400-500ms before it finally gives up, and I believe that this will only be worse on systems with even more memory. In certain contexts this delay is extremely harmful, so add a flag that will skip reclaim for allocation requests to allow those paths to opt-out of doing an expensive reclaim. Sponsored by: Dell Inc Differential Revision: https://reviews.freebsd.org/D28422 Reviewed by: markj, kib
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@ -54,6 +54,7 @@
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*/
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#define M_NOWAIT 0x0001 /* do not block */
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#define M_WAITOK 0x0002 /* ok to block */
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#define M_NORECLAIM 0x0080 /* do not reclaim after failure */
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#define M_ZERO 0x0100 /* bzero the allocation */
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#define M_NOVM 0x0200 /* don't ask VM for pages */
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#define M_USE_RESERVE 0x0400 /* can alloc out of reserve memory */
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@ -177,17 +177,22 @@ kmem_alloc_contig_pages(vm_object_t object, vm_pindex_t pindex, int domain,
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{
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vm_page_t m;
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int tries;
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bool wait;
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bool wait, reclaim;
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VM_OBJECT_ASSERT_WLOCKED(object);
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/* Disallow an invalid combination of flags. */
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MPASS((pflags & (VM_ALLOC_WAITOK | VM_ALLOC_NORECLAIM)) !=
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(VM_ALLOC_WAITOK | VM_ALLOC_NORECLAIM));
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wait = (pflags & VM_ALLOC_WAITOK) != 0;
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reclaim = (pflags & VM_ALLOC_NORECLAIM) == 0;
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pflags &= ~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL);
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pflags |= VM_ALLOC_NOWAIT;
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for (tries = wait ? 3 : 1;; tries--) {
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m = vm_page_alloc_contig_domain(object, pindex, domain, pflags,
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npages, low, high, alignment, boundary, memattr);
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if (m != NULL || tries == 0)
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if (m != NULL || tries == 0 || !reclaim)
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break;
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VM_OBJECT_WUNLOCK(object);
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@ -541,6 +541,7 @@ vm_page_t PHYS_TO_VM_PAGE(vm_paddr_t pa);
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#define VM_ALLOC_WAITFAIL 0x0010 /* (acf) Sleep and return error */
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#define VM_ALLOC_WIRED 0x0020 /* (acfgp) Allocate a wired page */
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#define VM_ALLOC_ZERO 0x0040 /* (acfgp) Allocate a prezeroed page */
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#define VM_ALLOC_NORECLAIM 0x0080 /* (c) Do not reclaim after failure */
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#define VM_ALLOC_NOOBJ 0x0100 /* (acg) No associated object */
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#define VM_ALLOC_NOBUSY 0x0200 /* (acgp) Do not excl busy the page */
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#define VM_ALLOC_NOCREAT 0x0400 /* (gp) Don't create a page */
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@ -570,6 +571,8 @@ malloc2vm_flags(int malloc_flags)
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pflags |= VM_ALLOC_NOWAIT;
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if ((malloc_flags & M_WAITOK))
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pflags |= VM_ALLOC_WAITOK;
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if ((malloc_flags & M_NORECLAIM))
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pflags |= VM_ALLOC_NORECLAIM;
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return (pflags);
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}
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#endif
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