Rewrite physio() to not allocate pbufs for unmapped I/O.
pbufs is a limited resource, and their allocator is not SMP-scalable. So instead of always allocating pbuf to immediately convert it to bio, allocate bio just here. If buffer needs kernel mapping, then pbuf is still allocated, but used only as a source of KVA and storage for a list of held pages. On 40-core system doing many 512-byte reads from user level to array of raw SSDs this change removes huge lock congestion inside pbuf allocator. It improves peak performance from ~300K to ~1.2M IOPS. On my previous 24-core system this problem also existed, but was less serious. Reviewed by: kib MFC after: 2 weeks
This commit is contained in:
Alexander Motin
parent
41c1a23326
commit
869fd29a7b
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=281825
@ -25,27 +25,26 @@ __FBSDID("$FreeBSD$");
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#include <sys/bio.h>
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#include <sys/buf.h>
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#include <sys/conf.h>
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#include <sys/malloc.h>
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#include <sys/proc.h>
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#include <sys/uio.h>
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#include <geom/geom.h>
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#include <vm/vm.h>
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#include <vm/vm_page.h>
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#include <vm/vm_extern.h>
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#include <vm/vm_map.h>
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int
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physio(struct cdev *dev, struct uio *uio, int ioflag)
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{
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struct buf *bp;
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struct cdevsw *csw;
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struct buf *pbuf;
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struct bio *bp;
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struct vm_page **pages;
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caddr_t sa;
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u_int iolen;
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int error, i, mapped;
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/* Keep the process UPAGES from being swapped. XXX: why ? */
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PHOLD(curproc);
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bp = getpbuf(NULL);
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sa = bp->b_data;
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error = 0;
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u_int iolen, poff;
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int error, i, npages, maxpages;
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vm_prot_t prot;
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/* XXX: sanity check */
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if(dev->si_iosize_max < PAGE_SIZE) {
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@ -76,95 +75,128 @@ physio(struct cdev *dev, struct uio *uio, int ioflag)
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uprintf("%s: request vectors=%d > 1; "
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"cannot split request\n", devtoname(dev),
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uio->uio_iovcnt);
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error = EFBIG;
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goto doerror;
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return (EFBIG);
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}
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/*
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* Keep the process UPAGES from being swapped. Processes swapped
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* out while holding pbufs, used by swapper, may lead to deadlock.
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*/
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PHOLD(curproc);
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bp = g_alloc_bio();
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if (uio->uio_segflg != UIO_USERSPACE) {
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pbuf = NULL;
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pages = NULL;
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} else if ((dev->si_flags & SI_UNMAPPED) && unmapped_buf_allowed) {
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pbuf = NULL;
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maxpages = btoc(MIN(uio->uio_resid, MAXPHYS)) + 1;
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pages = malloc(sizeof(*pages) * maxpages, M_DEVBUF, M_WAITOK);
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} else {
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pbuf = getpbuf(NULL);
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sa = pbuf->b_data;
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maxpages = btoc(MAXPHYS);
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pages = pbuf->b_pages;
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}
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prot = VM_PROT_READ;
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if (uio->uio_rw == UIO_READ)
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prot |= VM_PROT_WRITE; /* Less backwards than it looks */
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error = 0;
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for (i = 0; i < uio->uio_iovcnt; i++) {
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while (uio->uio_iov[i].iov_len) {
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bp->b_flags = 0;
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bzero(bp, sizeof(*bp));
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if (uio->uio_rw == UIO_READ) {
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bp->b_iocmd = BIO_READ;
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bp->bio_cmd = BIO_READ;
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curthread->td_ru.ru_inblock++;
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} else {
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bp->b_iocmd = BIO_WRITE;
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bp->bio_cmd = BIO_WRITE;
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curthread->td_ru.ru_oublock++;
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}
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bp->b_iodone = bdone;
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bp->b_data = uio->uio_iov[i].iov_base;
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bp->b_bcount = uio->uio_iov[i].iov_len;
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bp->b_offset = uio->uio_offset;
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bp->b_iooffset = uio->uio_offset;
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bp->b_saveaddr = sa;
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bp->bio_offset = uio->uio_offset;
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bp->bio_data = uio->uio_iov[i].iov_base;
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bp->bio_length = uio->uio_iov[i].iov_len;
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if (bp->bio_length > dev->si_iosize_max)
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bp->bio_length = dev->si_iosize_max;
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if (bp->bio_length > MAXPHYS)
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bp->bio_length = MAXPHYS;
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/* Don't exceed drivers iosize limit */
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if (bp->b_bcount > dev->si_iosize_max)
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bp->b_bcount = dev->si_iosize_max;
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/*
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* Make sure the pbuf can map the request
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* XXX: The pbuf has kvasize = MAXPHYS so a request
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* XXX: larger than MAXPHYS - PAGE_SIZE must be
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* XXX: page aligned or it will be fragmented.
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/*
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* Make sure the pbuf can map the request.
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* The pbuf has kvasize = MAXPHYS, so a request
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* larger than MAXPHYS - PAGE_SIZE must be
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* page aligned or it will be fragmented.
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*/
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iolen = ((vm_offset_t) bp->b_data) & PAGE_MASK;
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if ((bp->b_bcount + iolen) > bp->b_kvasize) {
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/*
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* This device does not want I/O to be split.
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*/
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poff = (vm_offset_t)bp->bio_data & PAGE_MASK;
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if (pbuf && bp->bio_length + poff > pbuf->b_kvasize) {
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if (dev->si_flags & SI_NOSPLIT) {
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uprintf("%s: request ptr %p is not "
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"on a page boundary; cannot split "
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"request\n", devtoname(dev),
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bp->b_data);
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bp->bio_data);
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error = EFBIG;
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goto doerror;
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}
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bp->b_bcount = bp->b_kvasize;
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if (iolen != 0)
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bp->b_bcount -= PAGE_SIZE;
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bp->bio_length = pbuf->b_kvasize;
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if (poff != 0)
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bp->bio_length -= PAGE_SIZE;
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}
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bp->b_bufsize = bp->b_bcount;
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bp->b_blkno = btodb(bp->b_offset);
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bp->bio_bcount = bp->bio_length;
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bp->bio_dev = dev;
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csw = dev->si_devsw;
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if (uio->uio_segflg == UIO_USERSPACE) {
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if (dev->si_flags & SI_UNMAPPED)
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mapped = 0;
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else
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mapped = 1;
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if (vmapbuf(bp, mapped) < 0) {
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if (pages) {
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if ((npages = vm_fault_quick_hold_pages(
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&curproc->p_vmspace->vm_map,
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(vm_offset_t)bp->bio_data, bp->bio_length,
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prot, pages, maxpages)) < 0) {
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error = EFAULT;
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goto doerror;
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}
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if (pbuf) {
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pmap_qenter((vm_offset_t)sa,
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pages, npages);
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bp->bio_data = sa + poff;
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} else {
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bp->bio_ma = pages;
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bp->bio_ma_n = npages;
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bp->bio_ma_offset = poff;
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bp->bio_data = unmapped_buf;
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bp->bio_flags |= BIO_UNMAPPED;
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}
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}
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dev_strategy_csw(dev, csw, bp);
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dev->si_devsw->d_strategy(bp);
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if (uio->uio_rw == UIO_READ)
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bwait(bp, PRIBIO, "physrd");
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biowait(bp, "physrd");
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else
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bwait(bp, PRIBIO, "physwr");
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biowait(bp, "physwr");
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if (uio->uio_segflg == UIO_USERSPACE)
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vunmapbuf(bp);
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iolen = bp->b_bcount - bp->b_resid;
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if (iolen == 0 && !(bp->b_ioflags & BIO_ERROR))
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if (pages) {
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if (pbuf)
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pmap_qremove((vm_offset_t)sa, npages);
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vm_page_unhold_pages(pages, npages);
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}
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iolen = bp->bio_length - bp->bio_resid;
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if (iolen == 0 && !(bp->bio_flags & BIO_ERROR))
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goto doerror; /* EOF */
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uio->uio_iov[i].iov_len -= iolen;
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uio->uio_iov[i].iov_base =
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(char *)uio->uio_iov[i].iov_base + iolen;
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uio->uio_resid -= iolen;
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uio->uio_offset += iolen;
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if( bp->b_ioflags & BIO_ERROR) {
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error = bp->b_error;
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if (bp->bio_flags & BIO_ERROR) {
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error = bp->bio_error;
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goto doerror;
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}
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}
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}
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doerror:
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relpbuf(bp, NULL);
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if (pbuf)
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relpbuf(pbuf, NULL);
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else if (pages)
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free(pages, M_DEVBUF);
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g_destroy_bio(bp);
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PRELE(curproc);
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return (error);
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}
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