From f357fcd890a8d6ced6d261338b859a41414561e9 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 7 Mar 2019 16:49:41 +0000 Subject: [PATCH] file-posix: add drop-cache=on|off option Commit dd577a26ff03b6829721b1ffbbf9e7c411b72378 ("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 Tested-by: Neil Skrypuch Reviewed-by: Stefano Garzarella Reviewed-by: Eric Blake Signed-off-by: Stefan Hajnoczi Message-id: 20190307164941.3322-1-stefanha@redhat.com Message-Id: <20190307164941.3322-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi --- block/file-posix.c | 16 ++++++++++++++++ qapi/block-core.json | 6 ++++++ 2 files changed, 22 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index ba6ab62a38..936dea8096 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -154,6 +154,7 @@ typedef struct BDRVRawState { bool page_cache_inconsistent:1; bool has_fallocate; bool needs_alignment; + bool drop_cache; bool check_cache_dropped; PRManager *pr_mgr; @@ -162,6 +163,7 @@ typedef struct BDRVRawState { typedef struct BDRVRawReopenState { int fd; int open_flags; + bool drop_cache; bool check_cache_dropped; } BDRVRawReopenState; @@ -422,6 +424,13 @@ static QemuOptsList raw_runtime_opts = { .type = QEMU_OPT_STRING, .help = "id of persistent reservation manager object (default: none)", }, +#if defined(__linux__) + { + .name = "drop-cache", + .type = QEMU_OPT_BOOL, + .help = "invalidate page cache during live migration (default: on)", + }, +#endif { .name = "x-check-cache-dropped", .type = QEMU_OPT_BOOL, @@ -511,6 +520,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options, } } + s->drop_cache = qemu_opt_get_bool(opts, "drop-cache", true); s->check_cache_dropped = qemu_opt_get_bool(opts, "x-check-cache-dropped", false); @@ -869,6 +879,7 @@ static int raw_reopen_prepare(BDRVReopenState *state, goto out; } + rs->drop_cache = qemu_opt_get_bool_del(opts, "drop-cache", true); rs->check_cache_dropped = qemu_opt_get_bool_del(opts, "x-check-cache-dropped", false); @@ -946,6 +957,7 @@ static void raw_reopen_commit(BDRVReopenState *state) BDRVRawState *s = state->bs->opaque; Error *local_err = NULL; + s->drop_cache = rs->drop_cache; s->check_cache_dropped = rs->check_cache_dropped; s->open_flags = rs->open_flags; @@ -2531,6 +2543,10 @@ static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs, return; } + if (!s->drop_cache) { + return; + } + if (s->open_flags & O_DIRECT) { return; /* No host kernel page cache */ } diff --git a/qapi/block-core.json b/qapi/block-core.json index 919d0530b2..ce91177bbc 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -2816,6 +2816,10 @@ # @locking: whether to enable file locking. If set to 'auto', only enable # when Open File Descriptor (OFD) locking API is available # (default: auto, since 2.10) +# @drop-cache: invalidate page cache during live migration. This prevents +# stale data on the migration destination with cache.direct=off. +# Currently only supported on Linux hosts. +# (default: on, since: 4.0) # @x-check-cache-dropped: whether to check that page cache was dropped on live # migration. May cause noticeable delays if the image # file is large, do not use in production. @@ -2828,6 +2832,8 @@ '*pr-manager': 'str', '*locking': 'OnOffAuto', '*aio': 'BlockdevAioOptions', + '*drop-cache': {'type': 'bool', + 'if': 'defined(CONFIG_LINUX)'}, '*x-check-cache-dropped': 'bool' } } ##