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De Francesco" Cc: =?iso-8859-1?B?Suly9G1l?= Glisse , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ira Weiny , Deepak R Varma , Sumitra Sharma Subject: Re: [PATCH v2] lib: Replace kmap() with kmap_local_page() Message-ID: <20230619164035.GC412243@sumitra.com> References: <20230610175712.GA348514@sumitra.com> <8275009.NyiUUSuA9g@suse> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8275009.NyiUUSuA9g@suse> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jun 18, 2023 at 06:50:04AM +0200, Fabio M. De Francesco wrote: > On sabato 10 giugno 2023 19:57:12 CEST Sumitra Sharma wrote: > > kmap() has been deprecated in favor of the kmap_local_page() > > due to high cost, restricted mapping space, the overhead of > > a global lock for synchronization, and making the process > > sleep in the absence of free slots. > > > > kmap_local_page() is faster than kmap() and offers thread-local > > and CPU-local mappings, take pagefaults in a local kmap region > > and preserves preemption by saving the mappings of outgoing > > tasks and restoring those of the incoming one during a context > > switch. > > > > The mappings are kept thread local in the functions > > “dmirror_do_read” and “dmirror_do_write” in test_hmm.c > > > > Therefore, replace kmap() with kmap_local_page() and use > > mempcy_from/to_page() to avoid open coding kmap_local_page() > > + memcpy() + kunmap_local(). > > > > Remove the unused variable “tmp”. > > > > > > Suggested-by: Fabio M. De Francesco > > LGTM, so... > > Reviewed-by: Fabio M. De Francesco > > Thanks, > > Fabio > > P.S.: The answer to an old question from you is that "LGTM" stands for "[It] > Looks Good To Me". > > It's just a way to introduce the "Reviewed-by" tag itself. However, "LGTM" is > not required, whereas the tag is required for a valid review and only the tag > line will be added by maintainers in the log when your patch gets applied. > > While here... Please don't put unnecessary blank lines between the tags.They > are not required and instead may worsen readability (obviously, I'm not > requiring a new version for this). > Hi Fabio, Thank you for your explanation and clarification regarding the meaning of "LGTM." I will take care of the blank lines. Thanks & regards Sumitra > > > > Signed-off-by: Sumitra Sharma > > --- > > > > Changes in v2: > > - Change commit subject and description. > > - Remove unnecessary type casting (char *). > > > > > > lib/test_hmm.c | 10 ++-------- > > 1 file changed, 2 insertions(+), 8 deletions(-) > > > > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > > index 67e6f83fe0f8..717dcb830127 100644 > > --- a/lib/test_hmm.c > > +++ b/lib/test_hmm.c > > @@ -368,16 +368,13 @@ static int dmirror_do_read(struct dmirror *dmirror, > > unsigned long start, for (pfn = start >> PAGE_SHIFT; pfn < (end >> > > PAGE_SHIFT); pfn++) { void *entry; > > struct page *page; > > - void *tmp; > > > > entry = xa_load(&dmirror->pt, pfn); > > page = xa_untag_pointer(entry); > > if (!page) > > return -ENOENT; > > > > - tmp = kmap(page); > > - memcpy(ptr, tmp, PAGE_SIZE); > > - kunmap(page); > > + memcpy_from_page(ptr, page, 0, PAGE_SIZE); > > > > ptr += PAGE_SIZE; > > bounce->cpages++; > > @@ -437,16 +434,13 @@ static int dmirror_do_write(struct dmirror *dmirror, > > unsigned long start, for (pfn = start >> PAGE_SHIFT; pfn < (end >> > > PAGE_SHIFT); pfn++) { void *entry; > > struct page *page; > > - void *tmp; > > > > entry = xa_load(&dmirror->pt, pfn); > > page = xa_untag_pointer(entry); > > if (!page || xa_pointer_tag(entry) != DPT_XA_TAG_WRITE) > > return -ENOENT; > > > > - tmp = kmap(page); > > - memcpy(tmp, ptr, PAGE_SIZE); > > - kunmap(page); > > + memcpy_to_page(page, 0, ptr, PAGE_SIZE); > > > > ptr += PAGE_SIZE; > > bounce->cpages++; > > -- > > 2.25.1 > > > >