From d9da70c7c6230b9698dc4a1dbc4d7f05794d2740 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Wed, 3 Aug 2022 12:42:52 +0200
Subject: kernel: reuse a single allocation for all vfs_requests of a process

$ iostress 32 512 0 > /vtty # before
512 calls, 0 bytes. avg 121133
$ iostress 32 512 0 > /vtty # after
512 calls, 0 bytes. avg 103540

103540/121133 = ~85%

I think the tiny bit of added complexity is worth it here.
---
 src/kernel/proc.c        |  9 +++++++--
 src/kernel/proc.h        |  6 +++---
 src/kernel/vfs/request.c | 44 ++++++++++++++++++++++----------------------
 src/kernel/vfs/request.h |  2 ++
 4 files changed, 34 insertions(+), 27 deletions(-)

(limited to 'src')

diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index a8cf303..e7a5ed6 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -114,8 +114,13 @@ void process_kill(struct process *p, int ret) {
 			p->controlled = NULL;
 		}
 
-		if (p->state == PS_WAITS4FS)
-			p->waits4fs.req->caller = NULL;
+		if (p->state == PS_WAITS4FS) {
+			assert(p->reqslot);
+			p->reqslot->caller = NULL; /* transfer ownership */
+			p->reqslot = NULL;
+		} else if (p->reqslot) {
+			kfree(p->reqslot);
+		}
 
 		if (p->state == PS_WAITS4PIPE) {
 			struct process **iter = &p->waits4pipe.pipe->pipe.queued;
diff --git a/src/kernel/proc.h b/src/kernel/proc.h
index c7e885a..d6f84bd 100644
--- a/src/kernel/proc.h
+++ b/src/kernel/proc.h
@@ -35,9 +35,6 @@ struct process {
 	// saved value, meaning depends on .state
 	union {
 		int death_msg; // PS_DEAD
-		struct {
-			struct vfs_request *req;
-		} waits4fs; // PS_WAITS4FS
 		struct {
 			char __user *buf;
 			size_t max_len;
@@ -52,6 +49,9 @@ struct process {
 	};
 	struct vfs_request *handled_req;
 
+	/* allocated once, the requests from WAITS4FS get stored here */
+	struct vfs_request *reqslot;
+
 	/* vfs_backend controlled (not exclusively) by this process */
 	struct vfs_backend *controlled;
 
diff --git a/src/kernel/vfs/request.c b/src/kernel/vfs/request.c
index 0164dfd..d942fba 100644
--- a/src/kernel/vfs/request.c
+++ b/src/kernel/vfs/request.c
@@ -8,29 +8,30 @@
 #include <shared/mem.h>
 
 void vfsreq_create(struct vfs_request req_) {
-	struct vfs_request *req = kmalloc(sizeof *req); // freed in vfsreq_finish
+	struct vfs_request *req;
+	if (req_.caller) {
+		process_transition(req_.caller, PS_WAITS4FS);
+		if (!req_.caller->reqslot)
+			req_.caller->reqslot = kmalloc(sizeof *req);
+		req = req_.caller->reqslot;
+		/* (re)using a single allocation for all request a process makes */
+	} else {
+		req = kmalloc(sizeof *req);
+	}
 	memcpy(req, &req_, sizeof *req);
 
 	if (req->backend)
 		req->backend->refcount++;
 
-	if (req->caller) {
-		// TODO after running `run_tests` from vga, this is entered with state == PS_WAITS4FS
-		process_transition(req->caller, PS_WAITS4FS);
-		req->caller->waits4fs.req = req;
-	}
-
-	if (!req->backend || !req->backend->potential_handlers) {
+	if (req->backend && req->backend->potential_handlers) {
+		struct vfs_request **iter = &req->backend->queue;
+		while (*iter != NULL) // find free spot in queue
+			iter = &(*iter)->queue_next;
+		*iter = req;
+		vfs_backend_tryaccept(req->backend);
+	} else {
 		vfsreq_finish_short(req, -1);
-		return;
 	}
-
-	struct vfs_request **iter = &req->backend->queue;
-	while (*iter != NULL) // find free spot in queue
-		iter = &(*iter)->queue_next;
-	*iter = req;
-
-	vfs_backend_tryaccept(req->backend);
 }
 
 void vfsreq_finish(struct vfs_request *req, char __user *stored, long ret,
@@ -70,17 +71,16 @@ void vfsreq_finish(struct vfs_request *req, char __user *stored, long ret,
 	if (req->input.kern)
 		kfree(req->input.buf_kern);
 
+	if (req->backend)
+		vfs_backend_refdown(req->backend);
+
 	if (req->caller) {
 		assert(req->caller->state == PS_WAITS4FS);
 		regs_savereturn(&req->caller->regs, ret);
 		process_transition(req->caller, PS_RUNNING);
+	} else {
+		kfree(req);
 	}
-
-	if (req->backend)
-		vfs_backend_refdown(req->backend);
-
-	kfree(req);
-	return;
 }
 
 void vfs_backend_tryaccept(struct vfs_backend *backend) {
diff --git a/src/kernel/vfs/request.h b/src/kernel/vfs/request.h
index cb560c9..ee33623 100644
--- a/src/kernel/vfs/request.h
+++ b/src/kernel/vfs/request.h
@@ -51,6 +51,8 @@ struct vfs_request {
 	long offset;
 	int flags;
 
+	/* if caller != NULL, owned by it - don't free, the allocation will be reused
+	 * if caller == NULL, free on finish */
 	struct process *caller;
 	struct vfs_backend *backend;
 
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