On Sun, Nov 12, 2017 at 9:54 AM, Jeff King <peff@xxxxxxxx> wrote: > On Sat, Nov 11, 2017 at 01:06:46PM -0500, Gargi Sharma wrote: > >> Replace custom allocation in mru.[ch] with generic calls >> to list.h API. >> >> Signed-off-by: Gargi Sharma <gs051095@xxxxxxxxx> > > Thanks, and welcome to the git list. :) > > This looks like a good start on the topic, but I have a few comments. > > It's a good idea to explain in the commit message not just what we're > doing, but why we want to do it, to help later readers of "git log". I > know that you picked this up from the discussion in the thread at: > > https://public-inbox.org/git/xmqq8tgz13x7.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > so it might be a good idea to summarize the ideas there (and add your > own thoughts, of course). > >> --- >> builtin/pack-objects.c | 14 ++++++++------ >> cache.h | 9 +++++---- >> mru.c | 27 --------------------------- >> mru.h | 40 ---------------------------------------- >> packfile.c | 28 +++++++++++++++++++--------- >> 5 files changed, 32 insertions(+), 86 deletions(-) >> delete mode 100644 mru.c >> delete mode 100644 mru.h > > After the "---" line, you can put any information that people on the > list might want to know but that doesn't need to go into the commit > message. The big thing the maintainer would want to know here is that > your patch is prepared on top of the ot/mru-on-list topic, so he knows > where to apply it. > > The diffstat is certainly encouraging so far. :) > >> @@ -1012,9 +1012,9 @@ static int want_object_in_pack(const unsigned char *sha1, >> return want; >> } >> >> - list_for_each(pos, &packed_git_mru.list) { >> - struct mru *entry = list_entry(pos, struct mru, list); >> - struct packed_git *p = entry->item; >> + list_for_each(pos, &packed_git_mru) { >> + struct packed_git *p = list_entry(pos, struct packed_git, mru); >> + struct list_head *entry = &(p->mru); >> off_t offset; >> >> if (p == *found_pack) > > I think "entry" here is going to be the same as "pos". That said, I > think it's only use is in bumping us to the front of the mru list later: > >> @@ -1030,8 +1030,10 @@ static int want_object_in_pack(const unsigned char *sha1, >> *found_pack = p; >> } >> want = want_found_object(exclude, p); >> - if (!exclude && want > 0) >> - mru_mark(&packed_git_mru, entry); >> + if (!exclude && want > 0) { >> + list_del(entry); >> + list_add(entry, &packed_git_mru); >> + } > > And I think this might be more obvious if we drop "entry" entirely and > just do: > > list_del(&p->mru); > list_add(&p->mru, &packed_git_mru); > > It might merit a comment like "/* bump to the front of the mru list */" > or similar to make it clear what's going on (or even adding a > list_move_to_front() helper). I will add a helper to list.h, for doing this :) > >> @@ -1566,6 +1566,7 @@ struct pack_window { >> >> extern struct packed_git { >> struct packed_git *next; >> + struct list_head mru; >> struct pack_window *windows; >> off_t pack_size; >> const void *index_data; > > Sort of a side note, but seeing these two list pointers together makes > me wonder what we should do with the list created by the "next" pointer. > It seems like there are three options: > > 1. Convert it to "struct list_head", too, for consistency. > > 2. Leave it as-is. We never delete from the list nor do any fancy > manipulation, so it doesn't benefit from the reusable code. > > 3. I wonder if we could drop it entirely, and just keep a single list > of packs, ordered by mru. I'm not sure if anybody actually cares > about accessing them in the "original" order. That order is > reverse-chronological (by prepare_packed_git()), but I think that > was mostly out of a sense that recent packs would be accessed more > than older ones (but having a real mru strategy replaces that > anyway). > > What do you think? I think in the long run, it'll be easier if there is only a single list of packs given that no one needs to access the list in order. If we go down road 1/3, would it be better if I sent an entirely different patch or a patch series with patch 1 as removing mru[.ch] and patch 2 as removing next pointer from the struct? > >> diff --git a/mru.c b/mru.c >> deleted file mode 100644 >> index 8f3f34c..0000000 > > Yay, this hunk (and the one for mru.h) is satisfying. > >> @@ -40,7 +40,7 @@ static unsigned int pack_max_fds; >> static size_t peak_pack_mapped; >> static size_t pack_mapped; >> struct packed_git *packed_git; >> -struct mru packed_git_mru = {{&packed_git_mru.list, &packed_git_mru.list}}; >> +LIST_HEAD(packed_git_mru); > > Much nicer. > >> @@ -859,9 +859,18 @@ static void prepare_packed_git_mru(void) >> { >> struct packed_git *p; >> >> - mru_clear(&packed_git_mru); >> - for (p = packed_git; p; p = p->next) >> - mru_append(&packed_git_mru, p); >> + struct list_head *pos; >> + struct list_head *tmp; >> + list_for_each_safe(pos, tmp, &packed_git_mru) >> + list_del_init(pos); > > This matches the original code, which did the clear/re-create, resetting > the mru to the "original" pack order. But I do wonder if that's actually > necessary. Could we skip that and just add any new packs to the list? But if we do not clear the older entries from the list, wouldn't there be a problem when you access packed_git_mru->next, since that will be populated instead of being empty? Or am I misunderstanding something here? > > That goes hand-in-hand with the idea of dropping the "next" pointer that > I mentioned above. > >> + INIT_LIST_HEAD(&packed_git_mru); > > I think this INIT_LIST_HEAD() isn't necessary anymore. In the original > code, we just freed each of the mru_entry structs, which meant we had to > forcibly reset the list head to be empty. But here you've used > list_del_init(), so after deleting everything, packed_git_mru should > already be empty. > >> + for (p = packed_git; p; p = p->next) { >> + struct packed_git *cur = xmalloc(sizeof(*packed_git)); >> + cur = p; >> + list_add_tail(&cur->mru, &packed_git_mru); >> + } > > This malloc can go away. The original mru code kept a separate entry, > but now we don't need that. So here you're just leaking it when you > assign "cur = p" (in fact, I think you can get rid of cur entirely). Ah yes, I'll fix this. > >> @@ -1830,10 +1839,11 @@ int find_pack_entry(const unsigned char *sha1, struct pack_entry *e) >> if (!packed_git) >> return 0; >> >> - list_for_each(pos, &packed_git_mru.list) { >> - struct mru *p = list_entry(pos, struct mru, list); >> - if (fill_pack_entry(sha1, e, p->item)) { >> - mru_mark(&packed_git_mru, p); >> + list_for_each(pos, &packed_git_mru) { >> + struct packed_git *p = list_entry(pos, struct packed_git, mru); >> + if (fill_pack_entry(sha1, e, p)) { >> + list_del(&p->mru); >> + list_add(&p->mru, &packed_git_mru); >> return 1; >> } >> } > > And this hunk looks pretty good (though if we added a move-to-front > helper, it could be used here, too). Thanks! gargi > > -Peff
