The branch main has been updated by 0mp: URL: https://cgit.FreeBSD.org/src/commit/?id=d01183fddf37b15da7ab3d69039e7759ae144451
commit d01183fddf37b15da7ab3d69039e7759ae144451 Author: Mateusz Piotrowski <[email protected]> AuthorDate: 2025-09-26 07:08:30 +0000 Commit: Mateusz Piotrowski <[email protected]> CommitDate: 2025-11-11 16:06:59 +0000 geom/zero: Add support for unmapped I/O This patch adds support for unmapped I/O to gzero(4). Let's consider the following script to illustrate the change in gzero(4)'s behavior: ``` dd="dd if=/dev/gzero of=/dev/null bs=512 count=100000" dtrace -q -c "$dd" -n ' fbt::pmap_qenter:entry, fbt::uiomove_fromphys:entry, fbt::memset:entry /execname == "dd"/ { @[probefunc] = count(); } ' ``` Let's run that script 4 times: ``` ==> 1: unmapped I/O not supported (fallback to mapped I/O), kern.geom.zero.clear=1 51200000 bytes transferred in 1.795809 secs (28510829 bytes/sec) pmap_qenter 100000 memset 400011 ==> 2: unmapped I/O not supported (fallback to mapped I/O), kern.geom.zero.clear=0 51200000 bytes transferred in 0.701079 secs (73030337 bytes/sec) memset 300011 ==> 3: unmapped I/O supported, kern.geom.zero.clear=1 51200000 bytes transferred in 0.771680 secs (66348750 bytes/sec) uiomove_fromphys 100000 memset 300011 ==> 4: unmapped I/O supported, kern.geom.zero.clear=0 51200000 bytes transferred in 0.621303 secs (82407407 bytes/sec) memset 300011 ``` If kern.geom.zero.clear=0, then nothing really changes as no copying takes place. Otherwise, we see by adding unmapped I/O support we avoid calls to pmap_qenter(), which was called by GEOM to turn unmapped I/O requests into mapped ones before passing them for processing to gzero(4). Reviewed by: bnovkov, markj Approved by: bnovkov (mentor), markj (mentor) MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D52998 --- sys/geom/zero/g_zero.c | 82 ++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 63 insertions(+), 19 deletions(-) diff --git a/sys/geom/zero/g_zero.c b/sys/geom/zero/g_zero.c index 7952147d660a..25d462a9f918 100644 --- a/sys/geom/zero/g_zero.c +++ b/sys/geom/zero/g_zero.c @@ -3,6 +3,7 @@ * * Copyright (c) 2005 Pawel Jakub Dawidek <[email protected]> * All rights reserved. + * Copyright (c) 2025 Mateusz Piotrowski <[email protected]> * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions @@ -34,53 +35,97 @@ #include <sys/queue.h> #include <sys/sysctl.h> #include <sys/systm.h> +#include <sys/uio.h> +#include <sys/types.h> #include <geom/geom.h> #define G_ZERO_CLASS_NAME "ZERO" -static int g_zero_clear_sysctl(SYSCTL_HANDLER_ARGS); +static int g_zero_byte_sysctl(SYSCTL_HANDLER_ARGS); SYSCTL_DECL(_kern_geom); static SYSCTL_NODE(_kern_geom, OID_AUTO, zero, CTLFLAG_RW | CTLFLAG_MPSAFE, 0, "GEOM_ZERO stuff"); static int g_zero_clear = 1; -SYSCTL_PROC(_kern_geom_zero, OID_AUTO, clear, - CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, &g_zero_clear, 0, - g_zero_clear_sysctl, "I", +SYSCTL_INT(_kern_geom_zero, OID_AUTO, clear, + CTLFLAG_RWTUN, &g_zero_clear, 0, "Clear read data buffer"); static int g_zero_byte = 0; -SYSCTL_INT(_kern_geom_zero, OID_AUTO, byte, CTLFLAG_RWTUN, &g_zero_byte, 0, +static uint8_t g_zero_buffer[PAGE_SIZE]; +SYSCTL_PROC(_kern_geom_zero, OID_AUTO, byte, + CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, &g_zero_byte, 0, + g_zero_byte_sysctl, "I", "Byte (octet) value to clear the buffers with"); static struct g_provider *gpp; static int -g_zero_clear_sysctl(SYSCTL_HANDLER_ARGS) +g_zero_byte_sysctl(SYSCTL_HANDLER_ARGS) { int error; - error = sysctl_handle_int(oidp, &g_zero_clear, 0, req); + // XXX: Confirm that this is called on module load as well. + // XXX: Shouldn't we lock here to avoid changing the byte value if the + // driver is in the process of handling I/O? + error = sysctl_handle_int(oidp, &g_zero_byte, 0, req); if (error != 0 || req->newptr == NULL) return (error); - if (gpp == NULL) - return (ENXIO); - if (g_zero_clear) - gpp->flags &= ~G_PF_ACCEPT_UNMAPPED; - else - gpp->flags |= G_PF_ACCEPT_UNMAPPED; + memset(g_zero_buffer, g_zero_byte, PAGE_SIZE); return (0); } +static void +g_zero_fill_pages(struct bio *bp) +{ + struct iovec aiovec; + struct uio auio; + size_t length; + vm_offset_t offset; + + aiovec.iov_base = g_zero_buffer; + aiovec.iov_len = PAGE_SIZE; + auio.uio_iov = &aiovec; + auio.uio_iovcnt = 1; + auio.uio_offset = 0; + auio.uio_segflg = UIO_SYSSPACE; + auio.uio_rw = UIO_WRITE; + auio.uio_td = curthread; + + /* + * To handle the unmapped I/O request, we need to fill the pages in the + * bp->bio_ma array with the g_zero_byte value. However, instead of + * setting every byte individually, we use uiomove_fromphys() to fill a + * page at a time with g_zero_buffer. + */ + bp->bio_resid = bp->bio_length; + offset = bp->bio_ma_offset & PAGE_MASK; + for (int i = 0; i < bp->bio_ma_n && bp->bio_resid > 0; i++) { + length = MIN(PAGE_SIZE - offset, bp->bio_resid); + auio.uio_resid = length; + + (void)uiomove_fromphys(&bp->bio_ma[i], offset, length, &auio); + + offset = 0; + bp->bio_resid -= length; + } +} + + static void g_zero_start(struct bio *bp) { - int error = ENXIO; + int error; switch (bp->bio_cmd) { case BIO_READ: - if (g_zero_clear && (bp->bio_flags & BIO_UNMAPPED) == 0) - memset(bp->bio_data, g_zero_byte, bp->bio_length); + if (g_zero_clear) { + if ((bp->bio_flags & BIO_UNMAPPED) != 0) + g_zero_fill_pages(bp); + else + memset(bp->bio_data, g_zero_byte, + bp->bio_length); + } /* FALLTHROUGH */ case BIO_DELETE: case BIO_WRITE: @@ -106,9 +151,8 @@ g_zero_init(struct g_class *mp) gp->start = g_zero_start; gp->access = g_std_access; gpp = pp = g_new_providerf(gp, "%s", gp->name); - pp->flags |= G_PF_DIRECT_SEND | G_PF_DIRECT_RECEIVE; - if (!g_zero_clear) - pp->flags |= G_PF_ACCEPT_UNMAPPED; + pp->flags |= G_PF_ACCEPT_UNMAPPED | G_PF_DIRECT_SEND | + G_PF_DIRECT_RECEIVE; pp->mediasize = 1152921504606846976LLU; pp->sectorsize = 512; g_error_provider(pp, 0);
