From: Phillip Wood <phillip.wood123@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Victoria Dye" <vdye@github.com>,
phillip.wood@dunelm.org.uk,
"Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>,
git@vger.kernel.org, stolee@gmail.com, newren@gmail.com,
"Taylor Blau" <me@ttaylorr.com>,
"Bagas Sanjaya" <bagasdotme@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH v3 6/8] reset: make sparse-aware (except --mixed)
Date: Tue, 12 Oct 2021 11:16:09 +0100 [thread overview]
Message-ID: <cd62bf13-fdf1-af00-cc25-ef20abcfe152@gmail.com> (raw)
In-Reply-To: <xmqqlf30edvf.fsf@gitster.g>
On 10/10/2021 23:03, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
>
>> On 08/10/2021 19:31, Junio C Hamano wrote:
>>> Victoria Dye <vdye@github.com> writes:
>>>
>>>> Phillip Wood wrote:
>>>
>>>>> I was looking at the callers to prime_cache_tree() this morning
>>>>> and would like to suggest an alternative approach - just delete
>>>>> prime_cache_tree() and all of its callers!
>>> Do you mean the calls added by new patches without understanding
>>> what they are doing, or all calls to it?
>>
>> I mean all calls to prime_cache_tree() after having understood (or at
>> least thinking that I understand) what they are doing.
>
> Sorry, my statement was confusingly written. I meant "calls added
> by new patches, written by those who do not understand what
> prime_cache_tree() calls are doing", but after re-reading it, I
> think it could be taken to be referring to "you may be commenting
> without understanding what prime_cache_tree() calls are doing",
> which wasn't my intention.
Thanks for clarifying that, I had misunderstood what you had written.
>> (a) a successful call to unpack_trees() updates the cache tree
>>
>> (b) all the existing calls to prime_cache_tree() follow a successful
>> call to unpack_trees() and nothing touches in index in between the
>> call to unpack_trees() and prime_cache_tree().
>
> Ahh, OK.
>
> I think we originally avoided calling cache_tree_update() lightly
> (because it is essentially a "write-tree", a fairly heavy-weight
> operation, without I/O) and instead relied on prime_cache_tree() to
> get degraded cache-tree back into freshness.
>
> What I forgot was that 52fca218 (unpack-trees: populate cache-tree
> on successful merge, 2015-07-28) added cache_tree_update() there at
> the end of unpack_trees(). The commit covers quite a wide range of
> operations---the log message says "merge", but in fact anything that
> uses unpack_trees() including branch switching and the resetting of
> the index are affected, and they cause a full reconstruction of the
> cache tree by calling cache_tree_update().
>
> For most callers of prime_cache_tree(), like the ones in "git
> read-tree" and "git reset", it is immediately obvious that we just
> read from the same tree, and we should have everything from the tree
> and nothing else in the resulting index, so it is clear that the
> prime_cache_tree() call is recreating the same cache-tree
> information that we already should have computed ourselves, and
> these calls can go (or if "prime" is still cheaper than "update",
> these callers can pass an option to tell unpack_trees() to skip the
> cache_tree_update() call, because they will call "prime" immediately
> after).
I haven't really thought this through but could we teach unpack_trees()
to call prime_cache_tree() rather than cache_tree_update() when that
would be safe? For callers that use oneway_merge() merge it should
always be safe I think and it might be possible to modify twoway_merge()
to signal if the final tree in the index matches the second one passed
to it. We could have a more general mechanism for the callback to signal
if it is safe to prime the tree but I suspect the callers that are using
custom callbacks are not updating the whole tree.
Best Wishes
Phillip
> For other callers it is not immediately obvious, but I trust you are
> correctly reading the code ;-)
>
> Thanks.
>
>
>
next prev parent reply other threads:[~2021-10-12 10:16 UTC|newest]
Thread overview: 114+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-30 14:50 [PATCH 0/7] Sparse Index: integrate with reset Victoria Dye via GitGitGadget
2021-09-30 14:50 ` [PATCH 1/7] reset: behave correctly with sparse-checkout Kevin Willford via GitGitGadget
2021-09-30 18:34 ` Junio C Hamano
2021-10-01 14:55 ` Victoria Dye
2021-09-30 14:50 ` [PATCH 2/7] sparse-index: update command for expand/collapse test Victoria Dye via GitGitGadget
2021-09-30 19:17 ` Taylor Blau
2021-09-30 20:11 ` Victoria Dye
2021-09-30 21:32 ` Junio C Hamano
2021-09-30 22:59 ` Victoria Dye
2021-10-01 0:04 ` Junio C Hamano
2021-10-04 13:47 ` Victoria Dye
2021-10-01 9:14 ` Bagas Sanjaya
2021-09-30 14:50 ` [PATCH 3/7] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-09-30 14:50 ` [PATCH 4/7] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-09-30 14:50 ` [PATCH 5/7] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-09-30 14:51 ` [PATCH 6/7] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-10-01 15:03 ` Victoria Dye
2021-09-30 14:51 ` [PATCH 7/7] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-10-05 13:20 ` [PATCH v2 0/7] Sparse Index: integrate with reset Victoria Dye via GitGitGadget
2021-10-05 13:20 ` [PATCH v2 1/7] reset: behave correctly with sparse-checkout Kevin Willford via GitGitGadget
2021-10-05 19:30 ` Junio C Hamano
2021-10-05 21:59 ` Victoria Dye
2021-10-06 12:44 ` Junio C Hamano
2021-10-06 1:46 ` Elijah Newren
2021-10-06 20:09 ` Victoria Dye
2021-10-06 10:31 ` Bagas Sanjaya
2021-10-05 13:20 ` [PATCH v2 2/7] update-index: add --force-full-index option for expand/collapse test Victoria Dye via GitGitGadget
2021-10-06 2:00 ` Elijah Newren
2021-10-06 20:40 ` Victoria Dye
2021-10-08 3:42 ` Elijah Newren
2021-10-08 17:11 ` Junio C Hamano
2021-10-06 10:33 ` Bagas Sanjaya
2021-10-05 13:20 ` [PATCH v2 3/7] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-10-06 2:04 ` Elijah Newren
2021-10-05 13:20 ` [PATCH v2 4/7] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-10-06 2:15 ` Elijah Newren
2021-10-06 17:48 ` Junio C Hamano
2021-10-05 13:20 ` [PATCH v2 5/7] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-10-06 3:43 ` Elijah Newren
2021-10-06 20:56 ` Victoria Dye
2021-10-06 10:34 ` Bagas Sanjaya
2021-10-05 13:20 ` [PATCH v2 6/7] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-10-06 4:43 ` Elijah Newren
2021-10-07 14:34 ` Victoria Dye
2021-10-05 13:20 ` [PATCH v2 7/7] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-10-06 10:37 ` Bagas Sanjaya
2021-10-05 15:34 ` [PATCH v2 0/7] Sparse Index: integrate with reset Ævar Arnfjörð Bjarmason
2021-10-05 20:44 ` Victoria Dye
2021-10-06 5:46 ` Elijah Newren
2021-10-07 21:15 ` [PATCH v3 0/8] " Victoria Dye via GitGitGadget
2021-10-07 21:15 ` [PATCH v3 1/8] reset: rename is_missing to !is_in_reset_tree Victoria Dye via GitGitGadget
2021-10-07 21:15 ` [PATCH v3 2/8] reset: preserve skip-worktree bit in mixed reset Kevin Willford via GitGitGadget
2021-10-08 9:04 ` Junio C Hamano
2021-10-07 21:15 ` [PATCH v3 3/8] update-index: add --force-full-index option for expand/collapse test Victoria Dye via GitGitGadget
2021-10-08 2:50 ` Bagas Sanjaya
2021-10-08 5:24 ` Junio C Hamano
2021-10-08 15:47 ` Victoria Dye
2021-10-08 17:19 ` Junio C Hamano
2021-10-11 14:12 ` Derrick Stolee
2021-10-11 15:05 ` Victoria Dye
2021-10-11 15:24 ` Junio C Hamano
2021-10-07 21:15 ` [PATCH v3 4/8] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-10-07 21:15 ` [PATCH v3 5/8] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-10-07 21:15 ` [PATCH v3 6/8] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-10-08 11:09 ` Phillip Wood
2021-10-08 17:14 ` Victoria Dye
2021-10-08 18:31 ` Junio C Hamano
2021-10-09 11:18 ` Phillip Wood
2021-10-10 22:03 ` Junio C Hamano
2021-10-11 15:55 ` Victoria Dye
2021-10-11 16:16 ` Junio C Hamano
2021-10-12 10:16 ` Phillip Wood [this message]
2021-10-12 19:15 ` Junio C Hamano
2021-10-12 10:17 ` Phillip Wood
2021-10-07 21:15 ` [PATCH v3 7/8] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-11-20 22:02 ` Elijah Newren
2021-11-22 16:46 ` Victoria Dye
2021-10-07 21:15 ` [PATCH v3 8/8] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 0/8] Sparse Index: integrate with reset Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 1/8] reset: rename is_missing to !is_in_reset_tree Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 2/8] reset: preserve skip-worktree bit in mixed reset Victoria Dye via GitGitGadget
2021-10-22 4:19 ` Emily Shaffer
2021-10-25 15:59 ` Victoria Dye
2021-10-11 20:30 ` [PATCH v4 3/8] sparse-index: update command for expand/collapse test Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 4/8] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 5/8] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 6/8] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 7/8] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-10-11 20:30 ` [PATCH v4 8/8] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 0/8] Sparse Index: integrate with reset Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 1/8] reset: rename is_missing to !is_in_reset_tree Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 2/8] reset: preserve skip-worktree bit in mixed reset Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 3/8] sparse-index: update command for expand/collapse test Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 4/8] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 5/8] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 6/8] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-10-27 14:39 ` [PATCH v5 7/8] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-11-20 22:05 ` Elijah Newren
2021-11-22 16:54 ` Victoria Dye
2021-10-27 14:39 ` [PATCH v5 8/8] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-11-20 22:13 ` [PATCH v5 0/8] Sparse Index: integrate with reset Elijah Newren
2021-11-29 15:52 ` [PATCH v6 " Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 1/8] reset: rename is_missing to !is_in_reset_tree Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 2/8] reset: preserve skip-worktree bit in mixed reset Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 3/8] sparse-index: update command for expand/collapse test Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 4/8] reset: expand test coverage for sparse checkouts Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 5/8] reset: integrate with sparse index Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 6/8] reset: make sparse-aware (except --mixed) Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 7/8] reset: make --mixed sparse-aware Victoria Dye via GitGitGadget
2021-11-29 15:52 ` [PATCH v6 8/8] unpack-trees: improve performance of next_cache_entry Victoria Dye via GitGitGadget
2021-11-29 18:37 ` [PATCH v6 0/8] Sparse Index: integrate with reset Elijah Newren
2021-11-29 19:44 ` Victoria Dye
2021-11-30 3:59 ` Elijah Newren
2021-12-01 20:26 ` Ævar Arnfjörð Bjarmason
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