On Wed, Mar 23, 2022 at 7:18 AM Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> wrote: > > Remove much of this as a POC for exploring some of what I mentioned in > https://lore.kernel.org/git/220322.86mthinxnn.gmgdl@xxxxxxxxxxxxxxxxxxx/ > > This commit is obviously not what we *should* do as end-state, but > demonstrates what's needed (I think) for a bare-minimum implementation > of just the "bulk" syncing method for loose objects without the part > where we do the tmp-objdir.c dance. > > Performance with this is already quite promising. Benchmarking with: > > git hyperfine -L rev ns/batched-fsync,HEAD -s 'make CFLAGS=-O3' \ > -p 'rm -rf r.git && git init --bare r.git' \ > './git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' > > I.e. unpacking a small packfile (my dotfiles) yields, on a Linux > ramdisk: > > Benchmark 1: ./git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'ns/batched-fsync > Time (mean ± σ): 815.9 ms ± 8.2 ms [User: 522.9 ms, System: 287.9 ms] > Range (min … max): 805.6 ms … 835.9 ms 10 runs > > Benchmark 2: ./git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'HEAD > Time (mean ± σ): 779.4 ms ± 15.4 ms [User: 505.7 ms, System: 270.2 ms] > Range (min … max): 763.1 ms … 813.9 ms 10 runs > > Summary > './git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'HEAD' ran > 1.05 ± 0.02 times faster than './git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'ns/batched-fsync' > > Doing the same with "strace --summary-only", which probably helps to > emulate cases with slower syscalls is ~15% faster than using the > tmp-objdir indirection: > > Summary > 'strace --summary-only ./git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'HEAD' ran > 1.16 ± 0.01 times faster than 'strace --summary-only ./git -C r.git -c core.fsync=loose-object -c core.fsyncMethod=batch unpack-objects </tmp/pack-dotfiles.pack' in 'ns/batched-fsync' > > Which makes sense in terms of syscalls. In my case HEAD has ~101k > calls, and the parent topic is making ~129k calls, with around 2x the > number of unlink(), link() as expected. > > Of course some users will want to use the tmp-objdir.c method. So a > version of this commit could be rewritten to come earlier in the > series, with the "bulk" on top being optional. > > It seems to me that it's a much better strategy to do this whole thing > in close_loose_object() after passing down the new HASH_N_OBJECTS / > HASH_N_OBJECTS_FIRST / HASH_N_OBJECTS_LAST flags. > > Doing that for the "builtin/add.c" and "builtin/unpack-objects.c" code > having its {un,}plug_bulk_checkin() removed here is then just a matter > of passing down a similar set of flags indicating whether we're > dealing with N objects, and if so if we're dealing with the last one > or not. > > As we'll see in subsequent commits doing it this way also effortlessly > integrates with other HASH_* flags. E.g. for "update-index" the code > being rm'd here doesn't handle the interaction with > "HASH_WRITE_OBJECT" properly, but once we've moved all this sync > bootstrapping logic to close_loose_object() we'll never get to it if > we're not actually writing something. > > This code currently doesn't use the HASH_N_OBJECTS_FIRST flag, but > that's what we'd use later to optionally call tmp_objdir_create(). > > Aside: This also changes logic that was a bit confusing and repetitive > in close_loose_object(). Previously we'd first call > batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT) which is just as > shorthand for: > > fsync_components & FSYNC_COMPONENT_LOOSE_OBJECT && > fsync_method == FSYNC_METHOD_BATCH > > We'd then proceed to call > fsync_component_or_die(FSYNC_COMPONENT_LOOSE_OBJECT) later in the same > function, which is just a way of calling fsync_or_die() if: > > fsync_components & FSYNC_COMPONENT_LOOSE_OBJECT > > Now we instead just define a local "fsync_loose" variable by checking > "fsync_components & FSYNC_COMPONENT_LOOSE_OBJECT", which shows us that > the previous case of fsync_component_or_die(...)" could just be added > to the existing "fsync_object_files > 0" branch. > > Note: This commit reverts much of "core.fsyncmethod: batched disk > flushes for loose-objects". We'll set up new structures to bring what > it was doing back in a different way. I.e. to do the tmp-objdir > plug-in in object-file.c > > Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> > --- > builtin/unpack-objects.c | 2 -- > builtin/update-index.c | 4 --- > bulk-checkin.c | 74 ---------------------------------------- > bulk-checkin.h | 3 -- > cache.h | 5 --- > object-file.c | 37 ++++++++++++++------ > 6 files changed, 26 insertions(+), 99 deletions(-) > > diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c > index ec40c6fd966..93da436581b 100644 > --- a/builtin/unpack-objects.c > +++ b/builtin/unpack-objects.c > @@ -507,7 +507,6 @@ static void unpack_all(void) > if (!quiet) > progress = start_progress(_("Unpacking objects"), nr_objects); > CALLOC_ARRAY(obj_list, nr_objects); > - plug_bulk_checkin(); > oflags = nr_objects > 1 ? HASH_N_OBJECTS : 0; > for (i = 0; i < nr_objects; i++) { > int nth = i + 1; > @@ -517,7 +516,6 @@ static void unpack_all(void) > unpack_one(i, oflags | f); > display_progress(progress, nth); > } > - unplug_bulk_checkin(); > stop_progress(&progress); > > if (delta_list) > diff --git a/builtin/update-index.c b/builtin/update-index.c > index cbd2b0d633b..95ed3c47b2e 100644 > --- a/builtin/update-index.c > +++ b/builtin/update-index.c > @@ -1118,8 +1118,6 @@ int cmd_update_index(int argc, const char **argv, const char *prefix) > parse_options_start(&ctx, argc, argv, prefix, > options, PARSE_OPT_STOP_AT_NON_OPTION); > > - /* optimize adding many objects to the object database */ > - plug_bulk_checkin(); > while (ctx.argc) { > if (parseopt_state != PARSE_OPT_DONE) > parseopt_state = parse_options_step(&ctx, options, > @@ -1194,8 +1192,6 @@ int cmd_update_index(int argc, const char **argv, const char *prefix) > strbuf_release(&buf); > } > > - /* by now we must have added all of the new objects */ > - unplug_bulk_checkin(); > if (split_index > 0) { > if (git_config_get_split_index() == 0) > warning(_("core.splitIndex is set to false; " > diff --git a/bulk-checkin.c b/bulk-checkin.c > index a0dca79ba6a..577b135e39c 100644 > --- a/bulk-checkin.c > +++ b/bulk-checkin.c > @@ -3,20 +3,15 @@ > */ > #include "cache.h" > #include "bulk-checkin.h" > -#include "lockfile.h" > #include "repository.h" > #include "csum-file.h" > #include "pack.h" > #include "strbuf.h" > -#include "string-list.h" > -#include "tmp-objdir.h" > #include "packfile.h" > #include "object-store.h" > > static int bulk_checkin_plugged; > > -static struct tmp_objdir *bulk_fsync_objdir; > - > static struct bulk_checkin_state { > char *pack_tmp_name; > struct hashfile *f; > @@ -85,40 +80,6 @@ static void finish_bulk_checkin(struct bulk_checkin_state *state) > reprepare_packed_git(the_repository); > } > > -/* > - * Cleanup after batch-mode fsync_object_files. > - */ > -static void do_batch_fsync(void) > -{ > - struct strbuf temp_path = STRBUF_INIT; > - struct tempfile *temp; > - > - if (!bulk_fsync_objdir) > - return; > - > - /* > - * Issue a full hardware flush against a temporary file to ensure > - * that all objects are durable before any renames occur. The code in > - * fsync_loose_object_bulk_checkin has already issued a writeout > - * request, but it has not flushed any writeback cache in the storage > - * hardware or any filesystem logs. This fsync call acts as a barrier > - * to ensure that the data in each new object file is durable before > - * the final name is visible. > - */ > - strbuf_addf(&temp_path, "%s/bulk_fsync_XXXXXX", get_object_directory()); > - temp = xmks_tempfile(temp_path.buf); > - fsync_or_die(get_tempfile_fd(temp), get_tempfile_path(temp)); > - delete_tempfile(&temp); > - strbuf_release(&temp_path); > - > - /* > - * Make the object files visible in the primary ODB after their data is > - * fully durable. > - */ > - tmp_objdir_migrate(bulk_fsync_objdir); > - bulk_fsync_objdir = NULL; > -} > - > static int already_written(struct bulk_checkin_state *state, struct object_id *oid) > { > int i; > @@ -313,26 +274,6 @@ static int deflate_to_pack(struct bulk_checkin_state *state, > return 0; > } > > -void prepare_loose_object_bulk_checkin(void) > -{ > - if (bulk_checkin_plugged && !bulk_fsync_objdir) > - bulk_fsync_objdir = tmp_objdir_create("bulk-fsync"); > -} > - > -void fsync_loose_object_bulk_checkin(int fd, const char *filename) > -{ > - /* > - * If we have a plugged bulk checkin, we issue a call that > - * cleans the filesystem page cache but avoids a hardware flush > - * command. Later on we will issue a single hardware flush > - * before as part of do_batch_fsync. > - */ > - if (!bulk_fsync_objdir || > - git_fsync(fd, FSYNC_WRITEOUT_ONLY) < 0) { > - fsync_or_die(fd, filename); > - } > -} > - > int index_bulk_checkin(struct object_id *oid, > int fd, size_t size, enum object_type type, > const char *path, unsigned flags) > @@ -347,19 +288,6 @@ int index_bulk_checkin(struct object_id *oid, > void plug_bulk_checkin(void) > { > assert(!bulk_checkin_plugged); > - > - /* > - * A temporary object directory is used to hold the files > - * while they are not fsynced. > - */ > - if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT)) { > - bulk_fsync_objdir = tmp_objdir_create("bulk-fsync"); > - if (!bulk_fsync_objdir) > - die(_("Could not create temporary object directory for core.fsyncMethod=batch")); > - > - tmp_objdir_replace_primary_odb(bulk_fsync_objdir, 0); > - } > - > bulk_checkin_plugged = 1; > } > > @@ -369,6 +297,4 @@ void unplug_bulk_checkin(void) > bulk_checkin_plugged = 0; > if (bulk_checkin_state.f) > finish_bulk_checkin(&bulk_checkin_state); > - > - do_batch_fsync(); > } > diff --git a/bulk-checkin.h b/bulk-checkin.h > index 181d3447ff9..b26f3dc3b74 100644 > --- a/bulk-checkin.h > +++ b/bulk-checkin.h > @@ -6,9 +6,6 @@ > > #include "cache.h" > > -void prepare_loose_object_bulk_checkin(void); > -void fsync_loose_object_bulk_checkin(int fd, const char *filename); > - > int index_bulk_checkin(struct object_id *oid, > int fd, size_t size, enum object_type type, > const char *path, unsigned flags); > diff --git a/cache.h b/cache.h > index 72c91c91286..2f3831fa853 100644 > --- a/cache.h > +++ b/cache.h > @@ -1772,11 +1772,6 @@ void fsync_or_die(int fd, const char *); > int fsync_component(enum fsync_component component, int fd); > void fsync_component_or_die(enum fsync_component component, int fd, const char *msg); > > -static inline int batch_fsync_enabled(enum fsync_component component) > -{ > - return (fsync_components & component) && (fsync_method == FSYNC_METHOD_BATCH); > -} > - > ssize_t read_in_full(int fd, void *buf, size_t count); > ssize_t write_in_full(int fd, const void *buf, size_t count); > ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset); > diff --git a/object-file.c b/object-file.c > index cd0ddb49e4b..dbeb3df502d 100644 > --- a/object-file.c > +++ b/object-file.c > @@ -1886,19 +1886,37 @@ void hash_object_file(const struct git_hash_algo *algo, const void *buf, > hash_object_file_literally(algo, buf, len, type_name(type), oid); > } > > +static void sync_loose_object_batch(int fd, const char *filename, > + const unsigned oflags) > +{ > + const int last = oflags & HASH_N_OBJECTS_LAST; > + > + /* > + * We're doing a sync_file_range() (or equivalent) for 1..N-1 > + * objects, and then a "real" fsync() for N. On some OS's > + * enabling core.fsync=loose-object && core.fsyncMethod=batch > + * improves the performance by a lot. > + */ > + if (last || (!last && git_fsync(fd, FSYNC_WRITEOUT_ONLY) < 0)) > + fsync_or_die(fd, filename); > +} > + > /* Finalize a file on disk, and close it. */ > -static void close_loose_object(int fd, const char *filename) > +static void close_loose_object(int fd, const char *filename, > + const unsigned oflags) > { > + int fsync_loose; > + > if (the_repository->objects->odb->will_destroy) > goto out; > > - if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT)) > - fsync_loose_object_bulk_checkin(fd, filename); > - else if (fsync_object_files > 0) > + fsync_loose = fsync_components & FSYNC_COMPONENT_LOOSE_OBJECT; > + > + if (oflags & HASH_N_OBJECTS && fsync_loose && > + fsync_method == FSYNC_METHOD_BATCH) > + sync_loose_object_batch(fd, filename, oflags); > + else if (fsync_object_files > 0 || fsync_loose) > fsync_or_die(fd, filename); > - else > - fsync_component_or_die(FSYNC_COMPONENT_LOOSE_OBJECT, fd, > - filename); > > out: > if (close(fd) != 0) > @@ -1962,9 +1980,6 @@ static int write_loose_object(const struct object_id *oid, char *hdr, > static struct strbuf tmp_file = STRBUF_INIT; > static struct strbuf filename = STRBUF_INIT; > > - if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT)) > - prepare_loose_object_bulk_checkin(); > - > loose_object_path(the_repository, &filename, oid); > > fd = create_tmpfile(&tmp_file, filename.buf); > @@ -2015,7 +2030,7 @@ static int write_loose_object(const struct object_id *oid, char *hdr, > die(_("confused by unstable object source data for %s"), > oid_to_hex(oid)); > > - close_loose_object(fd, tmp_file.buf); > + close_loose_object(fd, tmp_file.buf, flags); > > if (mtime) { > struct utimbuf utb; > -- > 2.35.1.1428.g1c1a0152d61 > Fine. Doing this patch series as non-RFC, we could start from prior to my fsyncMethod=batch series.
