file-posix: add drop-cache=on|off option
Commit dd577a26ff
("block/file-posix:
implement bdrv_co_invalidate_cache() on Linux") introduced page cache
invalidation so that cache.direct=off live migration is safe on Linux.
The invalidation takes a significant amount of time when the file is
large and present in the page cache. Normally this is not the case for
cross-host live migration but it can happen when migrating between QEMU
processes on the same host.
On same-host migration we don't need to invalidate pages for correctness
anyway, so an option to skip page cache invalidation is useful. I
investigated optimizing invalidation and detecting same-host migration,
but both are hard to achieve so a user-visible option will suffice.
As a bonus this option means that the cache invalidation feature will
now be detectable by libvirt via QMP schema introspection.
Suggested-by: Neil Skrypuch <neil@tembosocial.com>
Tested-by: Neil Skrypuch <neil@tembosocial.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190307164941.3322-1-stefanha@redhat.com
Message-Id: <20190307164941.3322-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
parent
3f3bbfc7ce
commit
f357fcd890
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@ -154,6 +154,7 @@ typedef struct BDRVRawState {
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bool page_cache_inconsistent:1;
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bool page_cache_inconsistent:1;
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bool has_fallocate;
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bool has_fallocate;
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bool needs_alignment;
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bool needs_alignment;
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bool drop_cache;
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bool check_cache_dropped;
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bool check_cache_dropped;
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PRManager *pr_mgr;
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PRManager *pr_mgr;
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@ -162,6 +163,7 @@ typedef struct BDRVRawState {
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typedef struct BDRVRawReopenState {
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typedef struct BDRVRawReopenState {
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int fd;
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int fd;
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int open_flags;
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int open_flags;
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bool drop_cache;
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bool check_cache_dropped;
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bool check_cache_dropped;
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} BDRVRawReopenState;
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} BDRVRawReopenState;
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@ -422,6 +424,13 @@ static QemuOptsList raw_runtime_opts = {
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.type = QEMU_OPT_STRING,
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.type = QEMU_OPT_STRING,
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.help = "id of persistent reservation manager object (default: none)",
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.help = "id of persistent reservation manager object (default: none)",
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},
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},
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#if defined(__linux__)
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{
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.name = "drop-cache",
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.type = QEMU_OPT_BOOL,
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.help = "invalidate page cache during live migration (default: on)",
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},
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#endif
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{
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{
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.name = "x-check-cache-dropped",
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.name = "x-check-cache-dropped",
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.type = QEMU_OPT_BOOL,
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.type = QEMU_OPT_BOOL,
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@ -511,6 +520,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
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}
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}
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}
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}
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s->drop_cache = qemu_opt_get_bool(opts, "drop-cache", true);
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s->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
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s->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped",
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false);
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false);
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@ -869,6 +879,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
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goto out;
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goto out;
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}
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}
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rs->drop_cache = qemu_opt_get_bool_del(opts, "drop-cache", true);
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rs->check_cache_dropped =
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rs->check_cache_dropped =
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qemu_opt_get_bool_del(opts, "x-check-cache-dropped", false);
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qemu_opt_get_bool_del(opts, "x-check-cache-dropped", false);
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@ -946,6 +957,7 @@ static void raw_reopen_commit(BDRVReopenState *state)
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BDRVRawState *s = state->bs->opaque;
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BDRVRawState *s = state->bs->opaque;
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Error *local_err = NULL;
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Error *local_err = NULL;
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s->drop_cache = rs->drop_cache;
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s->check_cache_dropped = rs->check_cache_dropped;
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s->check_cache_dropped = rs->check_cache_dropped;
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s->open_flags = rs->open_flags;
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s->open_flags = rs->open_flags;
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@ -2531,6 +2543,10 @@ static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs,
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return;
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return;
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}
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}
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if (!s->drop_cache) {
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return;
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}
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if (s->open_flags & O_DIRECT) {
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if (s->open_flags & O_DIRECT) {
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return; /* No host kernel page cache */
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return; /* No host kernel page cache */
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}
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}
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@ -2816,6 +2816,10 @@
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# @locking: whether to enable file locking. If set to 'auto', only enable
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# @locking: whether to enable file locking. If set to 'auto', only enable
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# when Open File Descriptor (OFD) locking API is available
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# when Open File Descriptor (OFD) locking API is available
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# (default: auto, since 2.10)
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# (default: auto, since 2.10)
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# @drop-cache: invalidate page cache during live migration. This prevents
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# stale data on the migration destination with cache.direct=off.
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# Currently only supported on Linux hosts.
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# (default: on, since: 4.0)
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# @x-check-cache-dropped: whether to check that page cache was dropped on live
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# @x-check-cache-dropped: whether to check that page cache was dropped on live
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# migration. May cause noticeable delays if the image
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# migration. May cause noticeable delays if the image
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# file is large, do not use in production.
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# file is large, do not use in production.
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@ -2828,6 +2832,8 @@
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'*pr-manager': 'str',
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'*pr-manager': 'str',
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'*locking': 'OnOffAuto',
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'*locking': 'OnOffAuto',
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'*aio': 'BlockdevAioOptions',
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'*aio': 'BlockdevAioOptions',
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'*drop-cache': {'type': 'bool',
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'if': 'defined(CONFIG_LINUX)'},
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'*x-check-cache-dropped': 'bool' } }
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'*x-check-cache-dropped': 'bool' } }
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##
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##
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