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From: Eric Wong <e@80x24.org>
To: "René Scharfe" <l.s.r@web.de>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>
Subject: Re: [PATCH v2 5/5] oidtree: a crit-bit tree for odb_loose_cache
Date: Tue, 6 Jul 2021 23:21:59 +0000	[thread overview]
Message-ID: <20210706232159.GB8624@dcvr> (raw)
In-Reply-To: <ab757bce-3b51-afac-312c-ea2e883cf0bf@web.de>

René Scharfe <l.s.r@web.de> wrote:
> Am 29.06.21 um 22:53 schrieb Eric Wong:
> > --- a/alloc.c
> > +++ b/alloc.c
> > @@ -14,6 +14,7 @@
> >  #include "tree.h"
> >  #include "commit.h"
> >  #include "tag.h"
> > +#include "oidtree.h"
> >  #include "alloc.h"
> >
> >  #define BLOCKING 1024
> > @@ -123,6 +124,11 @@ void *alloc_commit_node(struct repository *r)
> >  	return c;
> >  }
> >
> > +void *alloc_from_state(struct alloc_state *alloc_state, size_t n)
> > +{
> > +	return alloc_node(alloc_state, n);
> > +}
> > +
> 
> Why extend alloc.c instead of using mem-pool.c?  (I don't know which fits
> better, but when you say "memory pool" and not use mem-pool.c I just have
> to ask..)

I didn't know mem-pool.c existed :x  (And I've always known
about alloc.c).

Perhaps we could merge them in another series to avoid further
confusion.

> > +void oidtree_insert(struct oidtree *ot, const struct object_id *oid)
> > +{
> > +	struct oidtree_node *on;
> > +
> > +	if (!ot->mempool)
> > +		ot->mempool = allocate_alloc_state();
> > +	if (!oid->algo)
> > +		BUG("oidtree_insert requires oid->algo");
> > +
> > +	on = alloc_from_state(ot->mempool, sizeof(*on) + sizeof(*oid));
> > +	oidcpy_with_padding((struct object_id *)on->n.k, oid);
> > +
> > +	/*
> > +	 * n.b. we shouldn't get duplicates, here, but we'll have
> > +	 * a small leak that won't be freed until oidtree_destroy
> > +	 */
> 
> Why shouldn't we get duplicates?  That depends on the usage of oidtree,
> right?  The current user is fine because we avoid reading the same loose
> object directory twice using the loose_objects_subdir_seen bitmap.

Yes, it reflects the current caller.

> The leak comes from the allocation above, which is not used in case we
> already have the key in the oidtree.  So we need memory for all
> candidates, not just the inserted candidates.  That's probably
> acceptable in most use cases.

Yes, I think the small, impossible-due-to-current-usage leak is
an acceptable trade off.

> We can do better by keeping track of the unnecessary allocation in
> struct oidtree and recycling it at the next insert attempt, however.
> That way we'd only waste at most one slot.

It'd involve maintaining a free list; which may be better
suited to being in alloc_state or mem_pool.  That would also
increase the size of a struct *somewhere* and add a small
amount of code complexity, too.

> > +	cb_insert(&ot->t, &on->n, sizeof(*oid));
> > +}
> > +
> > +int oidtree_contains(struct oidtree *ot, const struct object_id *oid)
> > +{
> > +	struct object_id k = { 0 };
> > +	size_t klen = sizeof(k);
> > +	oidcpy_with_padding(&k, oid);
> 
> Why initialize k; isn't oidcpy_with_padding() supposed to overwrite it
> completely?

Ah, I only added oidcpy_with_padding later into the development
of this patch.

> > +
> > +	if (oid->algo == GIT_HASH_UNKNOWN) {
> > +		k.algo = hash_algo_by_ptr(the_hash_algo);
> > +		klen -= sizeof(oid->algo);
> > +	}
> 
> This relies on the order of the members hash and algo in struct
> object_id to find a matching hash if we don't actually know algo.  It
> also relies on the absence of padding after algo.  Would something like
> this make sense?
> 
>    BUILD_ASSERT_OR_ZERO(offsetof(struct object_id, algo) + sizeof(k.algo) == sizeof(k));

Maybe... I think a static assertion that object_id.hash be the
first element of "struct object_id" is definitely needed, at
least.

> And why set k.algo to some arbitrary value if we ignore it anyway?  I.e.
> why not keep it GIT_HASH_UNKNOWN, as set by oidcpy_with_padding()?

Good point, shortening klen would've been all that was needed.

> > +void oidtree_each(struct oidtree *ot, const struct object_id *oid,
> > +			size_t oidhexlen, oidtree_iter fn, void *arg)
> > +{
> > +	size_t klen = oidhexlen / 2;
> > +	struct oidtree_iter_data x = { 0 };
> > +
> > +	x.fn = fn;
> > +	x.arg = arg;
> > +	x.algo = oid->algo;
> > +	if (oidhexlen & 1) {
> > +		x.last_byte = oid->hash[klen];
> > +		x.last_nibble_at = &klen;
> > +	}
> > +	cb_each(&ot->t, (const uint8_t *)oid, klen, iter, &x);
> > +}
> 
> Clamp oidhexlen at GIT_MAX_HEXSZ?  Or die?

I think an assertion would be enough, here.
init_object_disambiguation already clamps to the_hash_algo->hexsz

  reply	other threads:[~2021-07-06 23:22 UTC|newest]

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24  0:58 [PATCH] speed up alt_odb_usable() with many alternates Eric Wong
2021-06-27  2:47 ` [PATCH 0/5] optimizations for many odb alternates Eric Wong
2021-06-27  2:47   ` [PATCH 1/5] speed up alt_odb_usable() with many alternates Eric Wong
2021-06-27  2:47   ` [PATCH 2/5] avoid strlen via strbuf_addstr in link_alt_odb_entry Eric Wong
2021-06-27  2:47   ` [PATCH 3/5] make object_directory.loose_objects_subdir_seen a bitmap Eric Wong
2021-06-27 10:23     ` René Scharfe
2021-06-28 23:09       ` Eric Wong
2021-06-27  2:47   ` [PATCH 4/5] oidcpy_with_padding: constify `src' arg Eric Wong
2021-06-27  2:47   ` [PATCH 5/5] oidtree: a crit-bit tree for odb_loose_cache Eric Wong
2021-06-29 14:42     ` Junio C Hamano
2021-06-29 20:17       ` Eric Wong
2021-06-29 20:53   ` [PATCH v2 0/5] optimizations for many alternates Eric Wong
2021-07-07 23:10     ` [PATCH v3 " Eric Wong
2021-07-07 23:10     ` [PATCH v3 1/5] speed up alt_odb_usable() with " Eric Wong
2021-07-08  0:20       ` Junio C Hamano
2021-07-08  1:14         ` Eric Wong
2021-07-08  4:30           ` Junio C Hamano
2021-07-07 23:10     ` [PATCH v3 2/5] avoid strlen via strbuf_addstr in link_alt_odb_entry Eric Wong
2021-07-08  4:57       ` Junio C Hamano
2021-07-07 23:10     ` [PATCH v3 3/5] make object_directory.loose_objects_subdir_seen a bitmap Eric Wong
2021-07-07 23:10     ` [PATCH v3 4/5] oidcpy_with_padding: constify `src' arg Eric Wong
2021-07-07 23:10     ` [PATCH v3 5/5] oidtree: a crit-bit tree for odb_loose_cache Eric Wong
2021-06-29 20:53   ` [PATCH v2 1/5] speed up alt_odb_usable() with many alternates Eric Wong
2021-07-03 10:05     ` René Scharfe
2021-07-04  9:02       ` René Scharfe
2021-07-06 23:01       ` Eric Wong
2021-06-29 20:53   ` [PATCH v2 2/5] avoid strlen via strbuf_addstr in link_alt_odb_entry Eric Wong
2021-06-29 20:53   ` [PATCH v2 3/5] make object_directory.loose_objects_subdir_seen a bitmap Eric Wong
2021-06-29 20:53   ` [PATCH v2 4/5] oidcpy_with_padding: constify `src' arg Eric Wong
2021-06-29 20:53   ` [PATCH v2 5/5] oidtree: a crit-bit tree for odb_loose_cache Eric Wong
2021-07-04  9:02     ` René Scharfe
2021-07-06 23:21       ` Eric Wong [this message]
2021-07-04  9:32     ` Ævar Arnfjörð Bjarmason
2021-07-07 23:12       ` Eric Wong
2021-08-06 15:31     ` Andrzej Hunt
2021-08-06 17:53       ` René Scharfe
2021-08-07 22:49         ` Eric Wong
2021-08-09  1:35           ` Carlo Arenas
2021-08-09  1:38             ` [PATCH/RFC 0/3] pedantic errors in next Carlo Marcelo Arenas Belón
2021-08-09  1:38               ` [PATCH/RFC 1/3] oidtree: avoid nested struct oidtree_node Carlo Marcelo Arenas Belón
2021-08-09  1:38               ` [PATCH/RFC 2/3] object-store: avoid extra ';' from KHASH_INIT Carlo Marcelo Arenas Belón
2021-08-09 15:53                 ` Junio C Hamano
2021-08-09  1:38               ` [PATCH/RFC 3/3] ci: run a pedantic build as part of the GitHub workflow Carlo Marcelo Arenas Belón
2021-08-09 10:50                 ` Bagas Sanjaya
2021-08-09 22:03                   ` Carlo Arenas
2021-08-09 14:56                 ` Phillip Wood
2021-08-09 22:48                   ` Carlo Arenas
2021-08-10 15:24                     ` Phillip Wood
2021-08-10 18:25                       ` Junio C Hamano
2021-08-30 11:36                   ` Ævar Arnfjörð Bjarmason
2021-08-31 20:28                     ` Carlo Arenas
2021-08-31 20:51                       ` Ævar Arnfjörð Bjarmason
2021-08-31 23:54                         ` Carlo Arenas
2021-09-01  1:52                           ` Jeff King
2021-09-01 17:55                             ` Junio C Hamano
2021-08-30 11:40                 ` Ævar Arnfjörð Bjarmason
2021-09-01  9:19                 ` [RFC PATCH v2 0/4] developer: support pedantic Carlo Marcelo Arenas Belón
2021-09-01  9:19                   ` [RFC PATCH v2 1/4] developer: retire USE_PARENS_AROUND_GETTEXT_N support Carlo Marcelo Arenas Belón
2021-09-01  9:19                   ` [RFC PATCH v2 2/4] developer: enable pedantic by default Carlo Marcelo Arenas Belón
2021-09-01  9:19                   ` [RFC PATCH v2 3/4] developer: add an alternative script for detecting broken N_() Carlo Marcelo Arenas Belón
2021-09-01  9:19                   ` [RFC PATCH v2 4/4] developer: move detect-compiler out of the main directory Carlo Marcelo Arenas Belón
2021-09-01 10:10                   ` [RFC PATCH v2 0/4] developer: support pedantic Jeff King
2021-09-01 11:25                     ` [PATCH] gettext: remove optional non-standard parens in N_() definition Ævar Arnfjörð Bjarmason
2021-09-01 17:31                       ` Eric Sunshine
2021-09-02  9:13                       ` Jeff King
2021-09-02 19:19                       ` Junio C Hamano
2021-09-01 11:27                     ` [RFC PATCH v2 0/4] developer: support pedantic Ævar Arnfjörð Bjarmason
2021-09-01 18:03                       ` Carlo Arenas
2021-09-03 17:02                   ` [PATCH v3 0/3] support pedantic in developer mode Carlo Marcelo Arenas Belón
2021-09-03 17:02                     ` [PATCH v3 1/3] gettext: remove optional non-standard parens in N_() definition Carlo Marcelo Arenas Belón
2021-09-10 15:39                       ` Ævar Arnfjörð Bjarmason
2021-09-03 17:02                     ` [PATCH v3 2/3] win32: allow building with pedantic mode enabled Carlo Marcelo Arenas Belón
2021-09-03 18:47                       ` René Scharfe
2021-09-03 20:13                         ` Carlo Marcelo Arenas Belón
2021-09-03 20:32                           ` Junio C Hamano
2021-09-03 20:38                           ` René Scharfe
2021-09-04  9:37                             ` René Scharfe
2021-09-04 14:42                               ` Carlo Arenas
2021-09-27 23:04                       ` Jonathan Tan
2021-09-28  0:30                         ` Carlo Arenas
2021-09-28 16:50                           ` Jonathan Tan
2021-09-28 17:37                           ` Junio C Hamano
2021-09-28 20:16                             ` Jonathan Tan
2021-09-29  1:00                               ` Carlo Arenas
2021-09-29 15:55                                 ` Junio C Hamano
2021-09-03 17:02                     ` [PATCH v3 3/3] developer: enable pedantic by default Carlo Marcelo Arenas Belón
2021-09-05  7:54                     ` [PATCH v3 0/3] support pedantic in developer mode Ævar Arnfjörð Bjarmason
2021-08-09 16:44               ` [PATCH/RFC 0/3] pedantic errors in next Junio C Hamano
2021-08-09 20:10                 ` Eric Wong
2021-08-10  6:16                 ` Carlo Marcelo Arenas Belón
2021-08-10 19:30                   ` René Scharfe
2021-08-10 23:49                     ` Carlo Arenas
2021-08-11  0:57                       ` Carlo Arenas
2021-08-11 14:57                       ` René Scharfe
2021-08-11 17:20                         ` Junio C Hamano
2021-08-10 18:59             ` [PATCH v2 5/5] oidtree: a crit-bit tree for odb_loose_cache René Scharfe
2021-08-10 19:40           ` René Scharfe
2021-08-14 20:00       ` [PATCH] oidtree: avoid unaligned access to crit-bit tree René Scharfe
2021-08-16 19:11         ` Junio C Hamano

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