From 65a7814b2dbc10ea86610092f03d0c1df95d08ad Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 23 May 2024 14:28:02 -0400
Subject: opt: Don't raise RLIMIT_NOFILE if it would prevent using
posix_spawn()
If we raise RLIMIT_NOFILE, we have to lower it before calling exec() for
compatibility with select(). If posix_spawn() doesn't support that, we
fall back to fork(), which is quite a bit slower.
Therefore, if we're going to exec() on most files, it's better to keep
RLIMIT_NOFILE the same to avoid the fork() cost, even though it makes
bftw() somewhat slower.
---
src/ctx.c | 1 +
src/ctx.h | 2 ++
src/eval.c | 3 +++
src/opt.c | 16 ++++++++++++++++
4 files changed, 22 insertions(+)
diff --git a/src/ctx.c b/src/ctx.c
index 71fef98..fac501a 100644
--- a/src/ctx.c
+++ b/src/ctx.c
@@ -56,6 +56,7 @@ struct bfs_ctx *bfs_ctx_new(void) {
goto fail;
}
ctx->cur_nofile = ctx->orig_nofile;
+ ctx->raise_nofile = true;
ctx->users = bfs_users_new();
if (!ctx->users) {
diff --git a/src/ctx.h b/src/ctx.h
index fc3020c..b28a63c 100644
--- a/src/ctx.h
+++ b/src/ctx.h
@@ -102,6 +102,8 @@ struct bfs_ctx {
struct rlimit orig_nofile;
/** The current RLIMIT_NOFILE limits. */
struct rlimit cur_nofile;
+ /** Whether the fd limit should be raised. */
+ bool raise_nofile;
/** The current time. */
struct timespec now;
diff --git a/src/eval.c b/src/eval.c
index 2ca4a1f..8863e34 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1466,6 +1466,9 @@ done:
static int raise_fdlimit(struct bfs_ctx *ctx) {
rlim_t cur = ctx->orig_nofile.rlim_cur;
rlim_t max = ctx->orig_nofile.rlim_max;
+ if (!ctx->raise_nofile) {
+ max = cur;
+ }
rlim_t target = 64 << 10;
if (rlim_cmp(target, max) > 0) {
diff --git a/src/opt.c b/src/opt.c
index d1dee11..6704a46 100644
--- a/src/opt.c
+++ b/src/opt.c
@@ -2221,6 +2221,11 @@ static float estimate_stat_odds(struct bfs_ctx *ctx) {
return 1.0 - nostat_odds;
}
+/** Matches -(exec|ok) ... \; */
+static bool single_exec(const struct bfs_expr *expr) {
+ return expr->eval_fn == eval_exec && !(expr->exec->flags & BFS_EXEC_MULTI);
+}
+
int bfs_optimize(struct bfs_ctx *ctx) {
bfs_ctx_dump(ctx, DEBUG_OPT);
@@ -2299,6 +2304,17 @@ int bfs_optimize(struct bfs_ctx *ctx) {
opt_leave(&opt, "eager stat cost: ${ylw}%g${rs}\n", eager_cost);
}
+#ifndef POSIX_SPAWN_SETRLIMIT
+ // If bfs_spawn_setrlimit() would force us to use fork() over
+ // posix_spawn(), the extra cost may outweigh the benefit of a
+ // higher RLIMIT_NOFILE
+ float single_exec_odds = estimate_odds(ctx->expr, single_exec);
+ if (single_exec_odds >= 0.5) {
+ opt_enter(&opt, "single ${blu}-exec${rs} odds: ${ylw}%g${rs}\n", single_exec_odds);
+ ctx->raise_nofile = false;
+ opt_leave(&opt, "not raising RLIMIT_NOFILE\n");
+ }
+#endif
}
opt_leave(&opt, NULL);
--
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