From: Andrew Morton <akpm@linux-foundation.org>
To: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, Baoquan He <bhe@redhat.com>,
Uladzislau Rezki <urezki@gmail.com>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Liu Shixin <liushixin2@huawei.com>, Jiri Olsa <jolsa@kernel.org>
Subject: Re: [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock and vmap_block->lock
Date: Sun, 19 Mar 2023 13:10:47 -0700 [thread overview]
Message-ID: <20230319131047.174fa4e29cabe4371b298ed0@linux-foundation.org> (raw)
In-Reply-To: <6c7f1ac0aeb55faaa46a09108d3999e4595870d9.1679209395.git.lstoakes@gmail.com>
On Sun, 19 Mar 2023 07:09:31 +0000 Lorenzo Stoakes <lstoakes@gmail.com> wrote:
> vmalloc() is, by design, not permitted to be used in atomic context and
> already contains components which may sleep, so avoiding spin locks is not
> a problem from the perspective of atomic context.
>
> The global vmap_area_lock is held when the red/black tree rooted in
> vmap_are_root is accessed and thus is rather long-held and under
> potentially high contention. It is likely to be under contention for reads
> rather than write, so replace it with a rwsem.
>
> Each individual vmap_block->lock is likely to be held for less time but
> under low contention, so a mutex is not an outrageous choice here.
>
> A subset of test_vmalloc.sh performance results:-
>
> fix_size_alloc_test 0.40%
> full_fit_alloc_test 2.08%
> long_busy_list_alloc_test 0.34%
> random_size_alloc_test -0.25%
> random_size_align_alloc_test 0.06%
> ...
> all tests cycles 0.2%
>
> This represents a tiny reduction in performance that sits barely above
> noise.
>
> The reason for making this change is to build a basis for vread() to be
> usable asynchronously, this eliminating the need for a bounce buffer when
> copying data to userland in read_kcore() and allowing that to be converted
> to an iterator form.
>
I'm not understanding the final paragraph. How and where is vread()
used "asynchronously"?
next prev parent reply other threads:[~2023-03-19 20:10 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-19 7:09 [PATCH v2 0/4] convert read_kcore(), vread() to use iterators Lorenzo Stoakes
2023-03-19 7:09 ` [PATCH v2 1/4] fs/proc/kcore: Avoid bounce buffer for ktext data Lorenzo Stoakes
2023-03-20 9:58 ` David Hildenbrand
2023-03-19 7:09 ` [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock and vmap_block->lock Lorenzo Stoakes
2023-03-19 20:10 ` Andrew Morton [this message]
2023-03-19 20:29 ` Lorenzo Stoakes
2023-03-19 20:47 ` Matthew Wilcox
2023-03-19 21:16 ` Lorenzo Stoakes
2023-03-20 8:40 ` Lorenzo Stoakes
2023-03-20 7:54 ` Uladzislau Rezki
2023-03-20 8:25 ` Lorenzo Stoakes
2023-03-20 8:32 ` Uladzislau Rezki
2023-03-20 8:35 ` Lorenzo Stoakes
2023-03-20 11:20 ` Uladzislau Rezki
2023-03-21 1:09 ` Dave Chinner
2023-03-21 5:23 ` Uladzislau Rezki
2023-03-21 7:45 ` Lorenzo Stoakes
2023-03-21 8:54 ` Uladzislau Rezki
2023-03-21 10:05 ` Dave Chinner
2023-03-21 10:24 ` Uladzislau Rezki
2023-03-22 13:18 ` Uladzislau Rezki
2023-03-22 17:47 ` Matthew Wilcox
2023-03-22 18:01 ` Uladzislau Rezki
2023-03-22 19:15 ` Uladzislau Rezki
2023-03-23 12:47 ` Uladzislau Rezki
2023-03-24 5:25 ` Dave Chinner
2023-03-24 5:31 ` Matthew Wilcox
2023-03-27 0:38 ` Dave Chinner
2023-03-27 17:22 ` Uladzislau Rezki
2023-03-28 2:53 ` Dave Chinner
2023-03-28 12:40 ` Uladzislau Rezki
2023-03-19 7:09 ` [PATCH v2 3/4] fs/proc/kcore: convert read_kcore() to read_kcore_iter() Lorenzo Stoakes
2023-03-19 7:09 ` [PATCH v2 4/4] mm: vmalloc: convert vread() to vread_iter() Lorenzo Stoakes
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