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Message-ID: <6b6a4e1c-a9e9-9592-d5b4-3c9210c8b650@collabora.com>
Date: Fri, 28 Jul 2023 16:02:02 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Michał Mirosław <emmir@...gle.com>,
Paul Gofman <pgofman@...eweavers.com>
Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>,
Peter Xu <peterx@...hat.com>,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrei Vagin <avagin@...il.com>,
Danylo Mocherniuk <mdanylo@...gle.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Yang Shi <shy828301@...il.com>,
Vlastimil Babka <vbabka@...e.cz>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Yun Zhou <yun.zhou@...driver.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Alex Sierra <alex.sierra@....com>,
Matthew Wilcox <willy@...radead.org>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com,
Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: WIP: Performance improvements
We are optimizing for more performance. Please find the change-set below
for easy review before next revision and post your comments:
- Replace memcpy() with direct copy as it proving to be very expensive
- Don't check if PAGE_IS_FILE if no mask needs it as it is very
expensive to check per pte
- Add question in comment for discussion purpose
- Add fast path for exclusive WP for ptes
---
fs/proc/task_mmu.c | 54 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 43 insertions(+), 11 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 7e92c33635cab..879baf896ed0b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1757,37 +1757,51 @@ static int pagemap_release(struct inode *inode,
struct file *file)
PAGE_IS_HUGE)
#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
+#define MASKS_OF_INTEREST(a) (a.category_inverted | a.category_mask | \
+ a.category_anyof_mask | a.return_mask)
+
struct pagemap_scan_private {
struct pm_scan_arg arg;
+ unsigned long masks_of_interest;
unsigned long cur_vma_category;
struct page_region *vec_buf, cur_buf;
unsigned long vec_buf_len, vec_buf_index, found_pages, end_addr;
struct page_region __user *vec_out;
};
-static unsigned long pagemap_page_category(struct vm_area_struct *vma,
+static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
+ struct vm_area_struct *vma,
unsigned long addr, pte_t pte)
{
unsigned long categories = 0;
if (pte_present(pte)) {
- struct page *page = vm_normal_page(vma, addr, pte);
+ struct page *page;
categories |= PAGE_IS_PRESENT;
if (!pte_uffd_wp(pte))
categories |= PAGE_IS_WRITTEN;
- if (page && !PageAnon(page))
- categories |= PAGE_IS_FILE;
+
+ if (p->masks_of_interest & PAGE_IS_FILE) {
+ page = vm_normal_page(vma, addr, pte);
+ if (page && !PageAnon(page))
+ categories |= PAGE_IS_FILE;
+ }
+
if (is_zero_pfn(pte_pfn(pte)))
categories |= PAGE_IS_PFNZERO;
} else if (is_swap_pte(pte)) {
- swp_entry_t swp = pte_to_swp_entry(pte);
+ swp_entry_t swp;
categories |= PAGE_IS_SWAPPED;
if (!pte_swp_uffd_wp_any(pte))
categories |= PAGE_IS_WRITTEN;
- if (is_pfn_swap_entry(swp) && !PageAnon(pfn_swap_entry_to_page(swp)))
- categories |= PAGE_IS_FILE;
+
+ if (p->masks_of_interest & PAGE_IS_FILE) {
+ swp = pte_to_swp_entry(pte);
+ if (is_pfn_swap_entry(swp) && !PageAnon(pfn_swap_entry_to_page(swp)))
+ categories |= PAGE_IS_FILE;
+ }
}
return categories;
@@ -1957,9 +1971,7 @@ static bool pagemap_scan_push_range(unsigned long
categories,
if (p->vec_buf_index >= p->vec_buf_len)
return false;
- memcpy(&p->vec_buf[p->vec_buf_index], cur_buf,
- sizeof(*p->vec_buf));
- ++p->vec_buf_index;
+ p->vec_buf[p->vec_buf_index++] = *cur_buf;
}
cur_buf->start = addr;
@@ -2095,9 +2107,24 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd,
unsigned long start,
return 0;
}
+ if (!p->vec_buf) {
+ /* Fast path for performing exclusive WP */
+ for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
+ if (pte_uffd_wp(ptep_get(pte)))
+ continue;
+ make_uffd_wp_pte(vma, addr, pte);
+ if (!flush) {
+ start = addr;
+ flush = true;
+ }
+ }
+ ret = 0;
+ goto flush_and_return;
+ }
+
for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
unsigned long categories = p->cur_vma_category |
- pagemap_page_category(vma, addr, ptep_get(pte));
+ pagemap_page_category(p, vma, addr, ptep_get(pte));
unsigned long next = addr + PAGE_SIZE;
ret = pagemap_scan_output(categories, p, addr, &next);
@@ -2119,6 +2146,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd,
unsigned long start,
}
}
+flush_and_return:
if (flush)
flush_tlb_range(vma, start, addr);
@@ -2284,6 +2312,9 @@ static int pagemap_scan_init_bounce_buffer(struct
pagemap_scan_private *p)
* consecutive ranges that have the same categories returned across
* walk_page_range() calls.
*/
+ // Question: Increasing the vec_buf_len increases the execution speed.
+ // But it'll increase the memory needed to run the IOCTL. Can we do
something here?
+ // Right now only have space for 512 entries of page_region
p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,
p->arg.vec_len - 1);
p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),
@@ -2329,6 +2360,7 @@ static long do_pagemap_scan(struct mm_struct *mm,
unsigned long uarg)
if (ret)
return ret;
+ p.masks_of_interest = MASKS_OF_INTEREST(p.arg);
ret = pagemap_scan_init_bounce_buffer(&p);
if (ret)
return ret;
--
2.39.2
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