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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22ac7b62922sm89363805ad.51.2025.04.13.20.04.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 13 Apr 2025 20:04:56 -0700 (PDT) Message-ID: <63e2eafc-1004-4c12-9d90-39377b0071f3@suse.com> Date: Mon, 14 Apr 2025 12:34:52 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6/8] btrfs: store a kernel virtual address in struct sector_ptr To: Christoph Hellwig Cc: linux-btrfs@vger.kernel.org References: <20250409111055.3640328-1-hch@lst.de> <20250409111055.3640328-7-hch@lst.de> <0b3a6b18-ab19-4997-86dc-fd269b7b61da@suse.com> <20250410053413.GC30044@lst.de> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXVgBQkQ/lqxAAoJEMI9kfOh Jf6o+jIH/2KhFmyOw4XWAYbnnijuYqb/obGae8HhcJO2KIGcxbsinK+KQFTSZnkFxnbsQ+VY fvtWBHGt8WfHcNmfjdejmy9si2jyy8smQV2jiB60a8iqQXGmsrkuR+AM2V360oEbMF3gVvim 2VSX2IiW9KERuhifjseNV1HLk0SHw5NnXiWh1THTqtvFFY+CwnLN2GqiMaSLF6gATW05/sEd V17MdI1z4+WSk7D57FlLjp50F3ow2WJtXwG8yG8d6S40dytZpH9iFuk12Sbg7lrtQxPPOIEU rpmZLfCNJJoZj603613w/M8EiZw6MohzikTWcFc55RLYJPBWQ+9puZtx1DopW2jOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXWBBQkQ/lrSAAoJEMI9kfOhJf6o cakH+QHwDszsoYvmrNq36MFGgvAHRjdlrHRBa4A1V1kzd4kOUokongcrOOgHY9yfglcvZqlJ qfa4l+1oxs1BvCi29psteQTtw+memmcGruKi+YHD7793zNCMtAtYidDmQ2pWaLfqSaryjlzR /3tBWMyvIeWZKURnZbBzWRREB7iWxEbZ014B3gICqZPDRwwitHpH8Om3eZr7ygZck6bBa4MU o1XgbZcspyCGqu1xF/bMAY2iCDcq6ULKQceuKkbeQ8qxvt9hVxJC2W3lHq8dlK1pkHPDg9wO JoAXek8MF37R8gpLoGWl41FIUb3hFiu3zhDDvslYM4BmzI18QgQTQnotJH8= In-Reply-To: <20250410053413.GC30044@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/4/10 15:04, Christoph Hellwig 写道: > On Thu, Apr 10, 2025 at 08:04:25AM +0930, Qu Wenruo wrote: >> 在 2025/4/9 20:40, Christoph Hellwig 写道: >>> All data pointed to by struct sector_ptr is non-highmem kernel memory. >>> Simplify the code by using a void pointer instead of a page + offset >>> pair and dropping all the kmap calls. >> >> But the higher level bio from btrfs filemaps can have highmem pages. >> >> That's why we keep the kmap/kunmap. > > Where do filemap pages come into the raid code? As far as I can see > they are always copied, and the memory is only allocated in the raid > code. As seen in this code we have two direct allocations that I > convered to __get_free_page, and one case that uses the bulk page > allocator where I use page_address. Or did I miss something? The function sector_in_rbio() can force to use the sector_ptr in bio_sectors, and by default we use bio_sectors first. Thus all the kmap/kunmap pairs are needed for call sites that is grabbing the sector through sector_in_rbio(). This includes: - generate_pq_vertical() - rmw_assemble_write_bios() - verify_one_sector() for READ_REBUILD - recovery_vertical() for READ_REBUILD So I'm afraid we still need the kmap/kunmap for now. > >> Or is there a way to set the filemap to no use any highmem pages? > > You can restrict the allocation of a mapping to avoid highmem using > mapping_set_gfp_mask(). But that would not help with direct I/O IFF > user pages came into this code. Fine, my dream of getting rid of highmem inside btrfs is still really a dream... Thanks, Qu