linux-kernel - Re: [PATCH 11/15] mm/swap: add helper swap_offset

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Date:   Tue, 17 May 2022 16:39:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     NeilBrown <neilb@...e.de>, <willy@...radead.org>, <vbabka@...e.cz>,
        <dhowells@...hat.com>, <apopple@...dia.com>, <david@...hat.com>,
        <surenb@...gle.com>, <peterx@...hat.com>,
        <naoya.horiguchi@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/15] mm/swap: add helper swap_offset_available()

On Tue, 10 May 2022 10:03:19 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:

> On 2022/5/10 8:45, NeilBrown wrote:
> > On Mon, 09 May 2022, Miaohe Lin wrote:
> >> Add helper swap_offset_available() to remove some duplicated codes.
> >> Minor readability improvement.
> > 
> > I don't think that putting the spin_lock() inside the inline helper is
> > good for readability.
> > If the function was called
> >    swap_offset_available_and_locked()
> 
> Yes, swap_offset_available_and_locked should be more suitable as we do the spin_lock
> inside it. Will do this in next version.
> 

--- a/mm/swapfile.c~mm-swap-add-helper-swap_offset_available-fix
+++ a/mm/swapfile.c
@@ -775,7 +775,8 @@ static void set_cluster_next(struct swap
 	this_cpu_write(*si->cluster_next_cpu, next);
 }
 
-static inline bool swap_offset_available(struct swap_info_struct *si, unsigned long offset)
+static bool swap_offset_available_and_locked(struct swap_info_struct *si,
+					     unsigned long offset)
 {
 	if (data_race(!si->swap_map[offset])) {
 		spin_lock(&si->lock);
@@ -967,7 +968,7 @@ done:
 scan:
 	spin_unlock(&si->lock);
 	while (++offset <= READ_ONCE(si->highest_bit)) {
-		if (swap_offset_available(si, offset))
+		if (swap_offset_available_and_locked(si, offset))
 			goto checks;
 		if (unlikely(--latency_ration < 0)) {
 			cond_resched();
@@ -977,7 +978,7 @@ scan:
 	}
 	offset = si->lowest_bit;
 	while (offset < scan_base) {
-		if (swap_offset_available(si, offset))
+		if (swap_offset_available_and_locked(si, offset))
 			goto checks;
 		if (unlikely(--latency_ration < 0)) {
 			cond_resched();
_