From: Jonathan Tan <jonathantanmy@google.com>
To: me@ttaylorr.com
Cc: jonathantanmy@google.com, git@vger.kernel.org,
dstolee@microsoft.com, gitster@pobox.com, peff@peff.net,
martin.agren@gmail.com, szeder.dev@gmail.com
Subject: Re: [PATCH v2 23/24] pack-bitmap-write: relax unique rewalk condition
Date: Mon, 7 Dec 2020 10:19:09 -0800 [thread overview]
Message-ID: <20201207181909.3032039-1-jonathantanmy@google.com> (raw)
In-Reply-To: <X8fBHz2A82hxUzV8@nand.local>
> > > In an effort to discover a happy medium, this change reduces the walk
> > > for intermediate commits to only the first-parent history. This focuses
> > > the walk on how the histories converge, which still has significant
> > > reduction in repeat object walks. It is still possible to create
> > > quadratic behavior in this version, but it is probably less likely in
> > > realistic data shapes.
> >
> > Would this work? I agree that the width of the commit bitmasks would go
> > down (and there would also be fewer commit bitmasks generated, further
> > increasing the memory savings). But intuitively, if there is a commit
> > that is selected and only accessible through non-1st-parent links, then
> > any bitmaps generated for it cannot be contributed to its descendants
> > (since there was no descendant-to-ancestor walk that could reach it in
> > order to form the reverse edge).
>
> s/bitmaps/bitmasks.
I do mean bitmaps there - bitmasks are contributed to parents, but
bitmaps are contributed to descendants, if I remember correctly.
> We'll select commits independent of their first
> parent histories, and so in the situation that you're describing, if C
> reaches A only through non-1st-parent history, then A's bitmask will not
> contain the bits from C.
C is the descendant and A is the ancestor. Yes, A's bitmask will not
contain the bits from C.
> But when generating the reachability bitmap for C, we'll still find that
> we've generated a bitmap for A, and we can copy its bits directly.
Here is my contention - this can happen only if there is a reverse edge
from A to C, as far as I can tell, but such a reverse edge has not been
formed.
> If
> this differs from an ancestor P that _is_ in the first-parent history,
> then P pushed its bits to C before calling fill_bitmap_commit() through
> the reverse edges.
>
> > > Here is some data taken on a fresh clone of the kernel:
> > >
> > > | runtime (sec) | peak heap (GB) |
> > > | | |
> > > | from | with | from | with |
> > > | scratch | existing | scratch | existing |
> > > -----------+---------+----------+---------+-----------
> > > original | 64.044 | 83.241 | 2.088 | 2.194 |
> > > last patch | 44.811 | 27.828 | 2.289 | 2.358 |
> > > this patch | 100.641 | 35.560 | 2.152 | 2.224 |
> >
> > Hmm...the jump from 44 to 100 seems rather large.
>
> Indeed. It's ameliorated a little bit in the later patches. We are
> over-walking some objects (as in we are walking them multiple times),
> but the return we get is reducing the peak heap usage from what it was
> in the last patch.
>
> In the "unfathomably large" category, this makes things tractable.
Quoting from the next patch [1]:
> | runtime (sec) | peak heap (GB) |
> | | |
> | from | with | from | with |
> | scratch | existing | scratch | existing |
> -----------+---------+----------+---------+-----------
> last patch | 100.641 | 35.560 | 2.152 | 2.224 |
> this patch | 99.720 | 11.696 | 2.152 | 2.217 |
That is true, but it is not ameliorated much :-(
If you have steps to generate these timings, I would like to try
comparing the performance between all patches and all-except-23.
[1] https://lore.kernel.org/git/42399a1c2e52e1d055a2d0ad96af2ca4dce6b1a0.1605649533.git.me@ttaylorr.com/
next prev parent reply other threads:[~2020-12-07 18:21 UTC|newest]
Thread overview: 173+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-11 19:41 [PATCH 00/23] pack-bitmap: bitmap generation improvements Taylor Blau
2020-11-11 19:41 ` [PATCH 01/23] ewah/ewah_bitmap.c: grow buffer past 1 Taylor Blau
2020-11-22 19:36 ` Junio C Hamano
2020-11-23 16:22 ` Taylor Blau
2020-11-24 2:48 ` Jeff King
2020-11-24 2:51 ` Jeff King
2020-12-01 22:56 ` Taylor Blau
2020-11-11 19:41 ` [PATCH 02/23] pack-bitmap: fix header size check Taylor Blau
2020-11-12 17:39 ` Martin Ågren
2020-11-11 19:42 ` [PATCH 03/23] pack-bitmap: bounds-check size of cache extension Taylor Blau
2020-11-12 17:47 ` Martin Ågren
2020-11-13 4:57 ` Jeff King
2020-11-13 5:26 ` Martin Ågren
2020-11-13 21:29 ` Taylor Blau
2020-11-13 21:39 ` Jeff King
2020-11-13 21:49 ` Taylor Blau
2020-11-13 22:11 ` Jeff King
2020-11-11 19:42 ` [PATCH 04/23] t5310: drop size of truncated ewah bitmap Taylor Blau
2020-11-11 19:42 ` [PATCH 05/23] rev-list: die when --test-bitmap detects a mismatch Taylor Blau
2020-11-11 19:42 ` [PATCH 06/23] ewah: factor out bitmap growth Taylor Blau
2020-11-11 19:42 ` [PATCH 07/23] ewah: make bitmap growth less aggressive Taylor Blau
2020-11-22 20:32 ` Junio C Hamano
2020-11-23 16:49 ` Taylor Blau
2020-11-24 3:00 ` Jeff King
2020-11-24 20:11 ` Junio C Hamano
2020-11-11 19:43 ` [PATCH 08/23] ewah: implement bitmap_or() Taylor Blau
2020-11-22 20:34 ` Junio C Hamano
2020-11-23 16:52 ` Taylor Blau
2020-11-11 19:43 ` [PATCH 09/23] ewah: add bitmap_dup() function Taylor Blau
2020-11-11 19:43 ` [PATCH 10/23] pack-bitmap-write: reimplement bitmap writing Taylor Blau
2020-11-11 19:43 ` [PATCH 11/23] pack-bitmap-write: pass ownership of intermediate bitmaps Taylor Blau
2020-11-11 19:43 ` [PATCH 12/23] pack-bitmap-write: fill bitmap with commit history Taylor Blau
2020-11-11 19:43 ` [PATCH 13/23] bitmap: add bitmap_diff_nonzero() Taylor Blau
2020-11-11 19:43 ` [PATCH 14/23] commit: implement commit_list_contains() Taylor Blau
2020-11-11 19:43 ` [PATCH 15/23] t5310: add branch-based checks Taylor Blau
2020-11-11 20:58 ` Derrick Stolee
2020-11-11 21:04 ` Junio C Hamano
2020-11-15 23:26 ` Johannes Schindelin
2020-11-11 19:43 ` [PATCH 16/23] pack-bitmap-write: rename children to reverse_edges Taylor Blau
2020-11-11 19:43 ` [PATCH 17/23] pack-bitmap-write: build fewer intermediate bitmaps Taylor Blau
2020-11-13 22:23 ` SZEDER Gábor
2020-11-13 23:03 ` Jeff King
2020-11-14 6:23 ` Jeff King
2020-11-11 19:43 ` [PATCH 18/23] pack-bitmap-write: ignore BITMAP_FLAG_REUSE Taylor Blau
2020-11-11 19:44 ` [PATCH 19/23] pack-bitmap: factor out 'bitmap_for_commit()' Taylor Blau
2020-11-11 19:44 ` [PATCH 20/23] pack-bitmap: factor out 'add_commit_to_bitmap()' Taylor Blau
2020-11-11 19:44 ` [PATCH 21/23] pack-bitmap-write: use existing bitmaps Taylor Blau
2020-11-11 19:44 ` [PATCH 22/23] pack-bitmap-write: relax unique rewalk condition Taylor Blau
2020-11-11 19:44 ` [PATCH 23/23] pack-bitmap-write: better reuse bitmaps Taylor Blau
2020-11-17 21:46 ` [PATCH v2 00/24] pack-bitmap: bitmap generation improvements Taylor Blau
2020-11-17 21:46 ` [PATCH v2 01/24] ewah/ewah_bitmap.c: grow buffer past 1 Taylor Blau
2020-11-17 21:46 ` [PATCH v2 02/24] pack-bitmap: fix header size check Taylor Blau
2020-11-17 21:46 ` [PATCH v2 03/24] pack-bitmap: bounds-check size of cache extension Taylor Blau
2020-11-17 21:46 ` [PATCH v2 04/24] t5310: drop size of truncated ewah bitmap Taylor Blau
2020-11-17 21:46 ` [PATCH v2 05/24] rev-list: die when --test-bitmap detects a mismatch Taylor Blau
2020-11-17 21:46 ` [PATCH v2 06/24] ewah: factor out bitmap growth Taylor Blau
2020-11-17 21:47 ` [PATCH v2 07/24] ewah: make bitmap growth less aggressive Taylor Blau
2020-11-17 21:47 ` [PATCH v2 08/24] ewah: implement bitmap_or() Taylor Blau
2020-11-17 21:47 ` [PATCH v2 09/24] ewah: add bitmap_dup() function Taylor Blau
2020-11-17 21:47 ` [PATCH v2 10/24] pack-bitmap-write: reimplement bitmap writing Taylor Blau
2020-11-25 0:53 ` Jonathan Tan
2020-11-28 17:27 ` Taylor Blau
2020-11-17 21:47 ` [PATCH v2 11/24] pack-bitmap-write: pass ownership of intermediate bitmaps Taylor Blau
2020-11-25 1:00 ` Jonathan Tan
2020-11-17 21:47 ` [PATCH v2 12/24] pack-bitmap-write: fill bitmap with commit history Taylor Blau
2020-11-22 21:50 ` Junio C Hamano
2020-11-23 14:54 ` Derrick Stolee
2020-11-25 1:14 ` Jonathan Tan
2020-11-28 17:21 ` Taylor Blau
2020-11-30 18:33 ` Jonathan Tan
2020-11-17 21:47 ` [PATCH v2 13/24] bitmap: add bitmap_diff_nonzero() Taylor Blau
2020-11-22 22:01 ` Junio C Hamano
2020-11-23 20:19 ` Taylor Blau
2020-11-17 21:47 ` [PATCH v2 14/24] commit: implement commit_list_contains() Taylor Blau
2020-11-17 21:47 ` [PATCH v2 15/24] t5310: add branch-based checks Taylor Blau
2020-11-25 1:17 ` Jonathan Tan
2020-11-28 17:30 ` Taylor Blau
2020-11-17 21:47 ` [PATCH v2 16/24] pack-bitmap-write: rename children to reverse_edges Taylor Blau
2020-11-17 21:47 ` [PATCH v2 17/24] pack-bitmap.c: check reads more aggressively when loading Taylor Blau
2020-11-17 21:48 ` [PATCH v2 18/24] pack-bitmap-write: build fewer intermediate bitmaps Taylor Blau
2020-11-24 6:07 ` Jonathan Tan
2020-11-25 1:46 ` Jonathan Tan
2020-11-30 18:41 ` Derrick Stolee
2020-11-17 21:48 ` [PATCH v2 19/24] pack-bitmap-write: ignore BITMAP_FLAG_REUSE Taylor Blau
2020-12-02 7:13 ` Jonathan Tan
2020-11-17 21:48 ` [PATCH v2 20/24] pack-bitmap: factor out 'bitmap_for_commit()' Taylor Blau
2020-12-02 7:17 ` Jonathan Tan
2020-11-17 21:48 ` [PATCH v2 21/24] pack-bitmap: factor out 'add_commit_to_bitmap()' Taylor Blau
2020-12-02 7:20 ` Jonathan Tan
2020-11-17 21:48 ` [PATCH v2 22/24] pack-bitmap-write: use existing bitmaps Taylor Blau
2020-12-02 7:28 ` Jonathan Tan
2020-12-02 16:21 ` Taylor Blau
2020-11-17 21:48 ` [PATCH v2 23/24] pack-bitmap-write: relax unique rewalk condition Taylor Blau
2020-12-02 7:44 ` Jonathan Tan
2020-12-02 16:30 ` Taylor Blau
2020-12-07 18:19 ` Jonathan Tan [this message]
2020-12-07 18:43 ` Derrick Stolee
2020-12-07 18:45 ` Derrick Stolee
2020-12-07 18:48 ` Jeff King
2020-11-17 21:48 ` [PATCH v2 24/24] pack-bitmap-write: better reuse bitmaps Taylor Blau
2020-12-02 8:08 ` Jonathan Tan
2020-12-02 16:35 ` Taylor Blau
2020-12-02 18:22 ` Derrick Stolee
2020-12-02 18:25 ` Taylor Blau
2020-12-07 18:26 ` Jonathan Tan
2020-12-07 18:24 ` Jonathan Tan
2020-12-07 19:20 ` Derrick Stolee
2020-11-18 18:32 ` [PATCH v2 00/24] pack-bitmap: bitmap generation improvements SZEDER Gábor
2020-11-18 19:51 ` Taylor Blau
2020-11-22 2:17 ` Taylor Blau
2020-11-22 2:28 ` Taylor Blau
2020-11-20 6:34 ` Martin Ågren
2020-11-21 19:37 ` Junio C Hamano
2020-11-21 20:11 ` Martin Ågren
2020-11-22 2:31 ` Taylor Blau
2020-11-24 2:43 ` Jeff King
2020-12-01 23:04 ` Taylor Blau
2020-12-01 23:37 ` Jonathan Tan
2020-12-01 23:43 ` Taylor Blau
2020-12-02 8:11 ` Jonathan Tan
2020-12-08 0:04 ` [PATCH v3 " Taylor Blau
2020-12-08 0:04 ` [PATCH v3 01/24] ewah/ewah_bitmap.c: avoid open-coding ALLOC_GROW() Taylor Blau
2020-12-08 0:04 ` [PATCH v3 02/24] pack-bitmap: fix header size check Taylor Blau
2020-12-08 0:04 ` [PATCH v3 03/24] pack-bitmap: bounds-check size of cache extension Taylor Blau
2020-12-08 0:04 ` [PATCH v3 04/24] t5310: drop size of truncated ewah bitmap Taylor Blau
2020-12-08 0:04 ` [PATCH v3 05/24] rev-list: die when --test-bitmap detects a mismatch Taylor Blau
2020-12-08 0:04 ` [PATCH v3 06/24] ewah: factor out bitmap growth Taylor Blau
2020-12-08 0:04 ` [PATCH v3 07/24] ewah: make bitmap growth less aggressive Taylor Blau
2020-12-08 0:04 ` [PATCH v3 08/24] ewah: implement bitmap_or() Taylor Blau
2020-12-08 0:04 ` [PATCH v3 09/24] ewah: add bitmap_dup() function Taylor Blau
2020-12-08 0:04 ` [PATCH v3 10/24] pack-bitmap-write: reimplement bitmap writing Taylor Blau
2020-12-08 0:05 ` [PATCH v3 11/24] pack-bitmap-write: pass ownership of intermediate bitmaps Taylor Blau
2020-12-08 0:05 ` [PATCH v3 12/24] pack-bitmap-write: fill bitmap with commit history Taylor Blau
2020-12-08 0:05 ` [PATCH v3 13/24] bitmap: implement bitmap_is_subset() Taylor Blau
2020-12-08 0:05 ` [PATCH v3 14/24] commit: implement commit_list_contains() Taylor Blau
2020-12-08 0:05 ` [PATCH v3 15/24] t5310: add branch-based checks Taylor Blau
2020-12-08 0:05 ` [PATCH v3 16/24] pack-bitmap-write: rename children to reverse_edges Taylor Blau
2020-12-08 0:05 ` [PATCH v3 17/24] pack-bitmap.c: check reads more aggressively when loading Taylor Blau
2020-12-08 0:05 ` [PATCH v3 18/24] pack-bitmap-write: build fewer intermediate bitmaps Taylor Blau
2020-12-08 0:05 ` [PATCH v3 19/24] pack-bitmap-write: ignore BITMAP_FLAG_REUSE Taylor Blau
2020-12-08 0:05 ` [PATCH v3 20/24] pack-bitmap: factor out 'bitmap_for_commit()' Taylor Blau
2020-12-08 0:05 ` [PATCH v3 21/24] pack-bitmap: factor out 'add_commit_to_bitmap()' Taylor Blau
2020-12-08 0:05 ` [PATCH v3 22/24] pack-bitmap-write: use existing bitmaps Taylor Blau
2020-12-08 0:05 ` [PATCH v3 23/24] pack-bitmap-write: relax unique rewalk condition Taylor Blau
2020-12-08 0:05 ` [PATCH v3 24/24] pack-bitmap-write: better reuse bitmaps Taylor Blau
2020-12-08 20:56 ` [PATCH v3 00/24] pack-bitmap: bitmap generation improvements Junio C Hamano
2020-12-08 21:03 ` Taylor Blau
2020-12-08 22:03 ` Junio C Hamano
2020-12-08 22:03 ` [PATCH v4 " Taylor Blau
2020-12-08 22:03 ` [PATCH v4 01/24] ewah/ewah_bitmap.c: avoid open-coding ALLOC_GROW() Taylor Blau
2020-12-08 22:03 ` [PATCH v4 02/24] pack-bitmap: fix header size check Taylor Blau
2020-12-08 22:03 ` [PATCH v4 03/24] pack-bitmap: bounds-check size of cache extension Taylor Blau
2020-12-08 22:03 ` [PATCH v4 04/24] t5310: drop size of truncated ewah bitmap Taylor Blau
2020-12-08 22:03 ` [PATCH v4 05/24] rev-list: die when --test-bitmap detects a mismatch Taylor Blau
2020-12-08 22:03 ` [PATCH v4 06/24] ewah: factor out bitmap growth Taylor Blau
2020-12-08 22:03 ` [PATCH v4 07/24] ewah: make bitmap growth less aggressive Taylor Blau
2020-12-08 22:03 ` [PATCH v4 08/24] ewah: implement bitmap_or() Taylor Blau
2020-12-08 22:03 ` [PATCH v4 09/24] ewah: add bitmap_dup() function Taylor Blau
2020-12-08 22:03 ` [PATCH v4 10/24] pack-bitmap-write: reimplement bitmap writing Taylor Blau
2020-12-08 22:03 ` [PATCH v4 11/24] pack-bitmap-write: pass ownership of intermediate bitmaps Taylor Blau
2020-12-08 22:04 ` [PATCH v4 12/24] pack-bitmap-write: fill bitmap with commit history Taylor Blau
2020-12-08 22:04 ` [PATCH v4 13/24] bitmap: implement bitmap_is_subset() Taylor Blau
2020-12-08 22:04 ` [PATCH v4 14/24] commit: implement commit_list_contains() Taylor Blau
2020-12-08 22:04 ` [PATCH v4 15/24] t5310: add branch-based checks Taylor Blau
2020-12-08 22:04 ` [PATCH v4 16/24] pack-bitmap-write: rename children to reverse_edges Taylor Blau
2020-12-08 22:04 ` [PATCH v4 17/24] pack-bitmap.c: check reads more aggressively when loading Taylor Blau
2020-12-08 22:04 ` [PATCH v4 18/24] pack-bitmap-write: build fewer intermediate bitmaps Taylor Blau
2020-12-08 22:04 ` [PATCH v4 19/24] pack-bitmap-write: ignore BITMAP_FLAG_REUSE Taylor Blau
2020-12-08 22:04 ` [PATCH v4 20/24] pack-bitmap: factor out 'bitmap_for_commit()' Taylor Blau
2020-12-08 22:05 ` [PATCH v4 21/24] pack-bitmap: factor out 'add_commit_to_bitmap()' Taylor Blau
2020-12-08 22:05 ` [PATCH v4 22/24] pack-bitmap-write: use existing bitmaps Taylor Blau
2020-12-08 22:05 ` [PATCH v4 23/24] pack-bitmap-write: relax unique revwalk condition Taylor Blau
2020-12-08 22:05 ` [PATCH v4 24/24] pack-bitmap-write: better reuse bitmaps Taylor Blau
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