svn commit: r324794 - head/sys/vm
Konstantin Belousov
kib at FreeBSD.org
Fri Oct 20 08:32:38 UTC 2017
Author: kib
Date: Fri Oct 20 08:32:37 2017
New Revision: 324794
URL: https://svnweb.freebsd.org/changeset/base/324794
Log:
Do not overwrite clean blocks on pageout.
If filesystem block size is less than the page size, it is possible
that the page-out run contains partially clean pages. E.g., the chunk
of the page might be bdwrite()-ed, or some thread performed bwrite()
on a buffer which references a chunk of the paged out page. As
result, the assertion added in r319975, which checked that all pages
in the run are dirty, does not hold on such filesystems.
One solution is to remove the assert, but it is undesirable, because
we do overwrite the valid on-disk content. I cannot provide a scenario
where such write would corrupt the file data, but I do not like it on
principle. Another, in my opinion proper, solution is to only write
parts of the pages still marked dirty. The patch implements this, it
skips clean blocks and only writes the dirty block runs.
Note that due to clustering, write one page might clean other pages in
the run, so the next write range must be calculated only after the
current range is written out.
More, due to a possible invalidation, and the fact that the object
lock is dropped and reacquired before the checks, it is possible that
the whole page-out pages run appears to consist of only clean pages.
For this reason, it is impossible to assert that there is some work
for the pageout method to do (i.e. assert that there is at least one
dirty page in the run). But such clearing can only occur due to
invalidation, and not due to a parallel write, because we own the
vnode lock exclusive.
Reported by: fsu
In collaboration with: pho
Reviewed by: alc, markj
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Differential revision: https://reviews.freebsd.org/D12668
Modified:
head/sys/vm/vnode_pager.c
Modified: head/sys/vm/vnode_pager.c
==============================================================================
--- head/sys/vm/vnode_pager.c Fri Oct 20 08:25:49 2017 (r324793)
+++ head/sys/vm/vnode_pager.c Fri Oct 20 08:32:37 2017 (r324794)
@@ -1179,7 +1179,24 @@ vnode_pager_putpages(vm_object_t object, vm_page_t *m,
VM_OBJECT_WLOCK(object);
}
+static int
+vn_off2bidx(vm_ooffset_t offset)
+{
+ return ((offset & PAGE_MASK) / DEV_BSIZE);
+}
+
+static bool
+vn_dirty_blk(vm_page_t m, vm_ooffset_t offset)
+{
+
+ KASSERT(IDX_TO_OFF(m->pindex) <= offset &&
+ offset < IDX_TO_OFF(m->pindex + 1),
+ ("page %p pidx %ju offset %ju", m, (uintmax_t)m->pindex,
+ (uintmax_t)offset));
+ return ((m->dirty & ((vm_page_bits_t)1 << vn_off2bidx(offset))) != 0);
+}
+
/*
* This is now called from local media FS's to operate against their
* own vnodes if they fail to implement VOP_PUTPAGES.
@@ -1195,10 +1212,12 @@ vnode_pager_generic_putpages(struct vnode *vp, vm_page
{
vm_object_t object;
vm_page_t m;
- vm_ooffset_t poffset;
+ vm_ooffset_t maxblksz, next_offset, poffset, prev_offset;
struct uio auio;
struct iovec aiov;
+ off_t prev_resid, wrsz;
int count, error, i, maxsize, ncount, pgoff, ppscheck;
+ bool in_hole;
static struct timeval lastfail;
static int curfail;
@@ -1260,34 +1279,102 @@ vnode_pager_generic_putpages(struct vnode *vp, vm_page
for (i = ncount; i < count; i++)
rtvals[i] = VM_PAGER_BAD;
}
- for (i = 0; i < ncount - ((btoc(maxsize) & PAGE_MASK) != 0); i++)
- MPASS(ma[i]->dirty == VM_PAGE_BITS_ALL);
- VM_OBJECT_WUNLOCK(object);
- aiov.iov_base = NULL;
- aiov.iov_len = maxsize;
auio.uio_iov = &aiov;
- auio.uio_iovcnt = 1;
- auio.uio_offset = poffset;
auio.uio_segflg = UIO_NOCOPY;
auio.uio_rw = UIO_WRITE;
- auio.uio_resid = maxsize;
auio.uio_td = NULL;
- error = VOP_WRITE(vp, &auio, vnode_pager_putpages_ioflags(flags),
- curthread->td_ucred);
- VM_CNT_INC(v_vnodeout);
- VM_CNT_ADD(v_vnodepgsout, ncount);
+ maxblksz = roundup2(poffset + maxsize, DEV_BSIZE);
- ppscheck = 0;
- if (error != 0 && (ppscheck = ppsratecheck(&lastfail, &curfail, 1))
- != 0)
- printf("vnode_pager_putpages: I/O error %d\n", error);
- if (auio.uio_resid != 0 && (ppscheck != 0 ||
- ppsratecheck(&lastfail, &curfail, 1) != 0))
- printf("vnode_pager_putpages: residual I/O %zd at %ju\n",
- auio.uio_resid, (uintmax_t)ma[0]->pindex);
- for (i = 0; i < ncount; i++)
+ for (prev_offset = poffset; prev_offset < maxblksz;) {
+ /* Skip clean blocks. */
+ for (in_hole = true; in_hole && prev_offset < maxblksz;) {
+ m = ma[OFF_TO_IDX(prev_offset - poffset)];
+ for (i = vn_off2bidx(prev_offset);
+ i < sizeof(vm_page_bits_t) * NBBY &&
+ prev_offset < maxblksz; i++) {
+ if (vn_dirty_blk(m, prev_offset)) {
+ in_hole = false;
+ break;
+ }
+ prev_offset += DEV_BSIZE;
+ }
+ }
+ if (in_hole)
+ goto write_done;
+
+ /* Find longest run of dirty blocks. */
+ for (next_offset = prev_offset; next_offset < maxblksz;) {
+ m = ma[OFF_TO_IDX(next_offset - poffset)];
+ for (i = vn_off2bidx(next_offset);
+ i < sizeof(vm_page_bits_t) * NBBY &&
+ next_offset < maxblksz; i++) {
+ if (!vn_dirty_blk(m, next_offset))
+ goto start_write;
+ next_offset += DEV_BSIZE;
+ }
+ }
+start_write:
+ if (next_offset > poffset + maxsize)
+ next_offset = poffset + maxsize;
+
+ /*
+ * Getting here requires finding a dirty block in the
+ * 'skip clean blocks' loop.
+ */
+ MPASS(prev_offset < next_offset);
+
+ VM_OBJECT_WUNLOCK(object);
+ aiov.iov_base = NULL;
+ auio.uio_iovcnt = 1;
+ auio.uio_offset = prev_offset;
+ prev_resid = auio.uio_resid = aiov.iov_len = next_offset -
+ prev_offset;
+ error = VOP_WRITE(vp, &auio,
+ vnode_pager_putpages_ioflags(flags), curthread->td_ucred);
+
+ wrsz = prev_resid - auio.uio_resid;
+ if (wrsz == 0) {
+ if (ppsratecheck(&lastfail, &curfail, 1) != 0) {
+ vn_printf(vp, "vnode_pager_putpages: "
+ "zero-length write at %ju resid %zd\n",
+ auio.uio_offset, auio.uio_resid);
+ }
+ VM_OBJECT_WLOCK(object);
+ break;
+ }
+
+ /* Adjust the starting offset for next iteration. */
+ prev_offset += wrsz;
+ MPASS(auio.uio_offset == prev_offset);
+
+ ppscheck = 0;
+ if (error != 0 && (ppscheck = ppsratecheck(&lastfail,
+ &curfail, 1)) != 0)
+ vn_printf(vp, "vnode_pager_putpages: I/O error %d\n",
+ error);
+ if (auio.uio_resid != 0 && (ppscheck != 0 ||
+ ppsratecheck(&lastfail, &curfail, 1) != 0))
+ vn_printf(vp, "vnode_pager_putpages: residual I/O %zd "
+ "at %ju\n", auio.uio_resid,
+ (uintmax_t)ma[0]->pindex);
+ VM_OBJECT_WLOCK(object);
+ if (error != 0 || auio.uio_resid != 0)
+ break;
+ }
+write_done:
+ /* Mark completely processed pages. */
+ for (i = 0; i < OFF_TO_IDX(prev_offset - poffset); i++)
rtvals[i] = VM_PAGER_OK;
+ /* Mark partial EOF page. */
+ if (prev_offset == poffset + maxsize && (prev_offset & PAGE_MASK) != 0)
+ rtvals[i++] = VM_PAGER_OK;
+ /* Unwritten pages in range, free bonus if the page is clean. */
+ for (; i < ncount; i++)
+ rtvals[i] = ma[i]->dirty == 0 ? VM_PAGER_OK : VM_PAGER_ERROR;
+ VM_OBJECT_WUNLOCK(object);
+ VM_CNT_ADD(v_vnodepgsout, i);
+ VM_CNT_INC(v_vnodeout);
return (rtvals[0]);
}
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