[PATCH v4] untracked-cache: support '--untracked-files=all' if configured

From: Tao Klerks <tao@klerks.biz>

Untracked cache was originally designed to only work with '-untracked-files=normal', but this causes performance issues for UI tooling that wants to see "all" on a frequent basis. On the other hand, the conditions that prevented applicability to the "all" mode no longer seem to apply.

The disqualification of untracked cache has a particularly significant impact on Windows with the defaulted fscache, where the introduction of fsmonitor can make the first and costly directory-iteration happen in untracked file detection, single-threaded, rather than in preload-index on multiple threads. Improving the performance of a "normal" 'git status' run with fsmonitor can make 'git status --untracked-files=all' perform much worse.

To partially address this, align the supported directory flags for the stored untracked cache data with the git config. If a user specifies an '--untracked-files=' commandline parameter that does not align with their 'status.showuntrackedfiles' config value, then the untracked cache will be ignored - as it is for other unsupported situations like when a pathspec is specified.

If the previously stored flags no longer match the current configuration, but the currently-applicable flags do match the current configuration, then discard the previously stored untracked cache data.

For most users there will be no change in behavior. Users who need '--untracked-files=all' to perform well will now have the option of setting "status.showuntrackedfiles" to "all" for better / more consistent performance.

Users who need '--untracked-files=all' to perform well for their tooling AND prefer to avoid the verbosity of "all" when running git status explicitly without options... are out of luck for now (no change).

Users who have the "status.showuntrackedfiles" config set to "all" and yet frequently explicitly call 'git status --untracked-files=normal' (and use the untracked cache) are the only ones who will be disadvantaged by this change. Their "--untracked-files=normal" calls will, after this change, no longer use the untracked cache.

Signed-off-by: Tao Klerks <tao@klerks.biz>
---
    Support untracked cache with '--untracked-files=all' if configured
    
    Resending this patch from a few months ago (with better standards
    compliance) - it hasn't seen any comments yet, I would dearly love some
    eyes on this as the change can make a big difference to hundreds of
    windows users in my environment (and I'd really rather not start
    distributing customized git builds!)
    
    This patch aims to make it possible for users of the -uall flag to git
    status, either by preference or by need (eg UI tooling), to benefit from
    the untracked cache when they set their 'status.showuntrackedfiles'
    config setting to 'all'. This is very important for large repos in
    Windows.
    
    More detail on the change and context in the commit message, I assume
    repeating a verbose message here is discouraged.
    
    These changes result from a couple of conversations,
    81153d02-8e7a-be59-e709-e90cd5906f3a@jeffhostetler.com and
    CABPp-BFiwzzUgiTj_zu+vF5x20L0=1cf25cHwk7KZQj2YkVzXw@mail.gmail.com>.
    
    The test suite passes, but as a n00b I do have questions:
    
     * Is there any additional validation that could/should be done to
       confirm that "-uall" untracked data can be cached safely?
       * It looks safe from following the code
       * It seems from discussing briefly with Elijah Newren in the thread
         above that thare are no obvious red flags
       * Manual testing, explicitly and implicitly through months of use,
         yields no issues
     * Is it OK to check the repo configuration in the body of processing?
       It seems to be a rare pattern
     * Can anyone think of a way to test this change?

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-985%2FTaoK%2Ftaok-untracked-cache-with-uall-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-985/TaoK/taok-untracked-cache-with-uall-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/985

Range-diff vs v3:

 1:  49cf90bfab5 ! 1:  5da418e5c60 untracked-cache: support '--untracked-files=all' if configured
     @@ dir.c: static void set_untracked_ident(struct untracked_cache *uc)
       }
       
      -static void new_untracked_cache(struct index_state *istate)
     -+static unsigned configured_default_dir_flags(struct index_state *istate)
     ++static unsigned configured_default_dir_flags(struct repository *repo)
      +{
     -+	/* This logic is coordinated with the setting of these flags in
     ++	/*
     ++	 * This logic is coordinated with the setting of these flags in
      +	 * wt-status.c#wt_status_collect_untracked(), and the evaluation
      +	 * of the config setting in commit.c#git_status_config()
      +	 */
      +	char *status_untracked_files_config_value;
     -+	int config_outcome = repo_config_get_string(istate->repo,
     -+								"status.showuntrackedfiles",
     -+								&status_untracked_files_config_value);
     ++	int config_outcome = repo_config_get_string(repo,
     ++						    "status.showuntrackedfiles",
     ++						    &status_untracked_files_config_value);
      +	if (!config_outcome && !strcmp(status_untracked_files_config_value, "all")) {
      +		return 0;
      +	} else {
     @@ dir.c: static void new_untracked_cache(struct index_state *istate)
       	if (!istate->untracked) {
      -		new_untracked_cache(istate);
      +		new_untracked_cache(istate,
     -+				configured_default_dir_flags(istate));
     ++				    configured_default_dir_flags(istate->repo));
       	} else {
       		if (!ident_in_untracked(istate->untracked)) {
       			free_untracked_cache(istate->untracked);
      -			new_untracked_cache(istate);
      +			new_untracked_cache(istate,
     -+					configured_default_dir_flags(istate));
     ++					    configured_default_dir_flags(istate->repo));
       		}
       	}
       }
      @@ dir.c: void remove_untracked_cache(struct index_state *istate)
     + }
       
       static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *dir,
     - 						      int base_len,
     +-						      int base_len,
      -						      const struct pathspec *pathspec)
     -+						      const struct pathspec *pathspec,
     -+							  struct index_state *istate)
     ++							    int base_len,
     ++							    const struct pathspec *pathspec,
     ++							    struct index_state *istate)
       {
       	struct untracked_cache_dir *root;
       	static int untracked_cache_disabled = -1;
     -+	unsigned configured_dir_flags;
     - 
     - 	if (!dir->untracked)
     - 		return NULL;
      @@ dir.c: static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *d
       	if (base_len || (pathspec && pathspec->nr))
       		return NULL;
     @@ dir.c: static struct untracked_cache_dir *validate_untracked_cache(struct dir_st
       		return NULL;
       	}
       
     -+	/* We don't support using or preparing the untracked cache if
     ++	/*
     ++	 * We don't support using or preparing the untracked cache if
      +	 * the current effective flags don't match the configured
      +	 * flags.
      +	 */
     -+	configured_dir_flags = configured_default_dir_flags(istate);
     -+	if (dir->flags != configured_dir_flags)
     ++	if (dir->flags != configured_default_dir_flags(istate->repo))
      +		return NULL;
      +
     -+	/* If the untracked structure we received does not have the same flags
     ++	/*
     ++	 * If the untracked structure we received does not have the same flags
      +	 * as configured, but the configured flags do match the effective flags,
      +	 * then we need to reset / create a new "untracked" structure to match
      +	 * the new config.
     @@ dir.c: static struct untracked_cache_dir *validate_untracked_cache(struct dir_st
      +	 */
      +	if (dir->flags != dir->untracked->dir_flags) {
      +		free_untracked_cache(istate->untracked);
     -+		new_untracked_cache(istate, configured_dir_flags);
     ++		new_untracked_cache(istate, dir->flags);
      +		dir->untracked = istate->untracked;
      +	}
      +

 dir.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 70 insertions(+), 19 deletions(-)