Further refine the implementation of POSIX_FADV_NOREUSE.
First, extend the changes in r230782 to better handle the common case of using NOREUSE with sequential reads. A NOREUSE file descriptor will now track the last implicit DONTNEED request it made as a result of a NOREUSE read. If a subsequent NOREUSE read is adjacent to the previous range, it will apply the DONTNEED request to the entire range of both the previous read and the current read. The effect is that each read of a file accessed sequentially will apply the DONTNEED request to the entire range that has been read. This allows NOREUSE to properly handle misaligned reads by flushing each buffer to cache once it has been completely read. Second, apply the same changes made to read(2) by r230782 and this change to writes. This provides much better performance in the sequential write case as it allows writes to still be clustered. It also provides much better performance for misaligned writes. It does mean that NOREUSE will be generally ineffective for non-sequential writes as the current implementation relies on a future NOREUSE write's implicit DONTNEED request to flush the dirty buffer from the current write. MFC after: 2 weeks
This commit is contained in:
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=237274
@ -28,7 +28,7 @@
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.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd February 25, 2012
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.Dd June 19, 2012
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.Dt POSIX_FADVISE 2
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.Os
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.Sh NAME
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@ -84,10 +84,9 @@ specified range and future access to this data may require a read operation.
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.It Dv POSIX_FADV_NOREUSE
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Tells the system that the specified data will only be accessed once and
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then not reused.
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Accesses to data within the specified range are treated as if the file
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descriptor has the
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.Dv O_DIRECT
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flag enabled.
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The system may decrease the in-memory priority of data once it has been
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read or written.
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Future access to this data may require a read operation.
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.El
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.Sh RETURN VALUES
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.Rv -std posix_fadvise
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@ -4872,6 +4872,8 @@ kern_posix_fadvise(struct thread *td, int fd, off_t offset, off_t len,
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new->fa_advice = advice;
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new->fa_start = offset;
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new->fa_end = end;
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new->fa_prevstart = 0;
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new->fa_prevend = 0;
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fp->f_advice = new;
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new = fa;
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}
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@ -542,7 +542,7 @@ vn_read(fp, uio, active_cred, flags, td)
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int error, ioflag;
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struct mtx *mtxp;
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int advice, vfslocked;
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off_t offset;
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off_t offset, start, end;
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KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
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uio->uio_td, td));
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@ -607,9 +607,38 @@ vn_read(fp, uio, active_cred, flags, td)
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fp->f_nextoff = uio->uio_offset;
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VOP_UNLOCK(vp, 0);
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if (error == 0 && advice == POSIX_FADV_NOREUSE &&
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offset != uio->uio_offset)
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error = VOP_ADVISE(vp, offset, uio->uio_offset - 1,
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POSIX_FADV_DONTNEED);
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offset != uio->uio_offset) {
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/*
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* Use POSIX_FADV_DONTNEED to flush clean pages and
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* buffers for the backing file after a
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* POSIX_FADV_NOREUSE read(2). To optimize the common
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* case of using POSIX_FADV_NOREUSE with sequential
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* access, track the previous implicit DONTNEED
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* request and grow this request to include the
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* current read(2) in addition to the previous
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* DONTNEED. With purely sequential access this will
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* cause the DONTNEED requests to continously grow to
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* cover all of the previously read regions of the
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* file. This allows filesystem blocks that are
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* accessed by multiple calls to read(2) to be flushed
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* once the last read(2) finishes.
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*/
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start = offset;
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end = uio->uio_offset - 1;
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mtx_lock(mtxp);
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if (fp->f_advice != NULL &&
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fp->f_advice->fa_advice == POSIX_FADV_NOREUSE) {
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if (start != 0 && fp->f_advice->fa_prevend + 1 == start)
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start = fp->f_advice->fa_prevstart;
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else if (fp->f_advice->fa_prevstart != 0 &&
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fp->f_advice->fa_prevstart == end + 1)
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end = fp->f_advice->fa_prevend;
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fp->f_advice->fa_prevstart = start;
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fp->f_advice->fa_prevend = end;
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}
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mtx_unlock(mtxp);
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error = VOP_ADVISE(vp, start, end, POSIX_FADV_DONTNEED);
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}
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VFS_UNLOCK_GIANT(vfslocked);
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return (error);
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}
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@ -630,6 +659,7 @@ vn_write(fp, uio, active_cred, flags, td)
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int error, ioflag, lock_flags;
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struct mtx *mtxp;
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int advice, vfslocked;
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off_t offset, start, end;
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KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
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uio->uio_td, td));
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@ -664,6 +694,7 @@ vn_write(fp, uio, active_cred, flags, td)
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if ((flags & FOF_OFFSET) == 0)
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uio->uio_offset = fp->f_offset;
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advice = POSIX_FADV_NORMAL;
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mtxp = NULL;
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if (fp->f_advice != NULL) {
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mtxp = mtx_pool_find(mtxpool_sleep, fp);
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mtx_lock(mtxp);
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@ -676,19 +707,14 @@ vn_write(fp, uio, active_cred, flags, td)
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switch (advice) {
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case POSIX_FADV_NORMAL:
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case POSIX_FADV_SEQUENTIAL:
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case POSIX_FADV_NOREUSE:
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ioflag |= sequential_heuristic(uio, fp);
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break;
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case POSIX_FADV_RANDOM:
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/* XXX: Is this correct? */
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break;
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case POSIX_FADV_NOREUSE:
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/*
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* Request the underlying FS to discard the buffers
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* and pages after the I/O is complete.
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*/
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ioflag |= IO_DIRECT;
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break;
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}
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offset = uio->uio_offset;
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#ifdef MAC
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error = mac_vnode_check_write(active_cred, fp->f_cred, vp);
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@ -701,6 +727,55 @@ vn_write(fp, uio, active_cred, flags, td)
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VOP_UNLOCK(vp, 0);
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if (vp->v_type != VCHR)
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vn_finished_write(mp);
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if (error == 0 && advice == POSIX_FADV_NOREUSE &&
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offset != uio->uio_offset) {
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/*
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* Use POSIX_FADV_DONTNEED to flush clean pages and
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* buffers for the backing file after a
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* POSIX_FADV_NOREUSE write(2). To optimize the
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* common case of using POSIX_FADV_NOREUSE with
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* sequential access, track the previous implicit
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* DONTNEED request and grow this request to include
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* the current write(2) in addition to the previous
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* DONTNEED. With purely sequential access this will
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* cause the DONTNEED requests to continously grow to
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* cover all of the previously written regions of the
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* file.
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*
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* Note that the blocks just written are almost
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* certainly still dirty, so this only works when
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* VOP_ADVISE() calls from subsequent writes push out
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* the data written by this write(2) once the backing
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* buffers are clean. However, as compared to forcing
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* IO_DIRECT, this gives much saner behavior. Write
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* clustering is still allowed, and clean pages are
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* merely moved to the cache page queue rather than
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* outright thrown away. This means a subsequent
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* read(2) can still avoid hitting the disk if the
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* pages have not been reclaimed.
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*
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* This does make POSIX_FADV_NOREUSE largely useless
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* with non-sequential access. However, sequential
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* access is the more common use case and the flag is
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* merely advisory.
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*/
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start = offset;
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end = uio->uio_offset - 1;
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mtx_lock(mtxp);
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if (fp->f_advice != NULL &&
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fp->f_advice->fa_advice == POSIX_FADV_NOREUSE) {
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if (start != 0 && fp->f_advice->fa_prevend + 1 == start)
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start = fp->f_advice->fa_prevstart;
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else if (fp->f_advice->fa_prevstart != 0 &&
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fp->f_advice->fa_prevstart == end + 1)
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end = fp->f_advice->fa_prevend;
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fp->f_advice->fa_prevstart = start;
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fp->f_advice->fa_prevend = end;
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}
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mtx_unlock(mtxp);
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error = VOP_ADVISE(vp, start, end, POSIX_FADV_DONTNEED);
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}
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unlock:
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VFS_UNLOCK_GIANT(vfslocked);
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return (error);
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@ -126,6 +126,8 @@ struct fadvise_info {
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int fa_advice; /* (f) FADV_* type. */
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off_t fa_start; /* (f) Region start. */
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off_t fa_end; /* (f) Region end. */
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off_t fa_prevstart; /* (f) Previous NOREUSE start. */
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off_t fa_prevend; /* (f) Previous NOREUSE end. */
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};
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struct file {
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