From: Christoph Hellwig <hch@infradead.org> To: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Brandt <Chris.Brandt@renesas.com> Subject: Re: [PATCH v5 4/5] cramfs: add mmap support Date: Fri, 6 Oct 2017 00:00:38 -0700 [thread overview] Message-ID: <20171006070038.GA29142@infradead.org> (raw) In-Reply-To: <20171006024531.8885-5-nicolas.pitre@linaro.org> > + /* Don't map the last page if it contains some other data */ > + if (unlikely(pgoff + pages == max_pages)) { > + unsigned int partial = offset_in_page(inode->i_size); > + if (partial) { > + char *data = sbi->linear_virt_addr + offset; > + data += (max_pages - 1) * PAGE_SIZE + partial; > + if (memchr_inv(data, 0, PAGE_SIZE - partial) != NULL) { > + pr_debug("mmap: %s: last page is shared\n", > + file_dentry(file)->d_name.name); > + pages--; > + } > + } > + } Why is pgoff + pages == max_pages marked unlikely? Mapping the whole file seems like a perfectly normal and likely case to me.. Also if this was my code I'd really prefer to move this into a helper: static bool cramfs_mmap_last_page_is_shared(struct inode *inode, int offset) { unsigned int partial = offset_in_page(inode->i_size); char *data = CRAMFS_SB(inode->i_sb)->linear_virt_addr + offset + (inode->i_size & PAGE_MASK); return memchr_inv(data + partial, 0, PAGE_SIZE - partial); } if (pgoff + pages == max_pages && offset_in_page(inode->i_size) && cramfs_mmap_last_page_is_shared(inode, offset)) pages--; as that's much more readable and the function name provides a good documentation of what is going on. > + if (pages != vma_pages(vma)) { here is how I would turn this around: if (!pages) goto done; if (pages == vma_pages(vma)) { remap_pfn_range(); goto done; } ... for (i = 0; i < pages; i++) { ... vm_insert_mixed(); nr_mapped++; } done: pr_debug("mapped %d out ouf %d\n", ..); if (pages != vma_pages(vma)) vma->vm_ops = &generic_file_vm_ops; return 0; } In fact we probably could just set the vm_ops unconditionally, they just wouldn't be called, but that might be more confusing then helpful.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org> To: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Brandt <Chris.Brandt@renesas.com> Subject: Re: [PATCH v5 4/5] cramfs: add mmap support Date: Fri, 6 Oct 2017 00:00:38 -0700 [thread overview] Message-ID: <20171006070038.GA29142@infradead.org> (raw) In-Reply-To: <20171006024531.8885-5-nicolas.pitre@linaro.org> > + /* Don't map the last page if it contains some other data */ > + if (unlikely(pgoff + pages == max_pages)) { > + unsigned int partial = offset_in_page(inode->i_size); > + if (partial) { > + char *data = sbi->linear_virt_addr + offset; > + data += (max_pages - 1) * PAGE_SIZE + partial; > + if (memchr_inv(data, 0, PAGE_SIZE - partial) != NULL) { > + pr_debug("mmap: %s: last page is shared\n", > + file_dentry(file)->d_name.name); > + pages--; > + } > + } > + } Why is pgoff + pages == max_pages marked unlikely? Mapping the whole file seems like a perfectly normal and likely case to me.. Also if this was my code I'd really prefer to move this into a helper: static bool cramfs_mmap_last_page_is_shared(struct inode *inode, int offset) { unsigned int partial = offset_in_page(inode->i_size); char *data = CRAMFS_SB(inode->i_sb)->linear_virt_addr + offset + (inode->i_size & PAGE_MASK); return memchr_inv(data + partial, 0, PAGE_SIZE - partial); } if (pgoff + pages == max_pages && offset_in_page(inode->i_size) && cramfs_mmap_last_page_is_shared(inode, offset)) pages--; as that's much more readable and the function name provides a good documentation of what is going on. > + if (pages != vma_pages(vma)) { here is how I would turn this around: if (!pages) goto done; if (pages == vma_pages(vma)) { remap_pfn_range(); goto done; } ... for (i = 0; i < pages; i++) { ... vm_insert_mixed(); nr_mapped++; } done: pr_debug("mapped %d out ouf %d\n", ..); if (pages != vma_pages(vma)) vma->vm_ops = &generic_file_vm_ops; return 0; } In fact we probably could just set the vm_ops unconditionally, they just wouldn't be called, but that might be more confusing then helpful. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-10-06 7:00 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-06 2:45 [PATCH v5 0/5] cramfs refresh for embedded usage Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 2:45 ` [PATCH v5 1/5] cramfs: direct memory access support Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 2:45 ` [PATCH v5 2/5] cramfs: make cramfs_physmem usable as root fs Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 2:45 ` [PATCH v5 3/5] cramfs: implement uncompressed and arbitrary data block positioning Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 2:45 ` [PATCH v5 4/5] cramfs: add mmap support Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 7:00 ` Christoph Hellwig [this message] 2017-10-06 7:00 ` Christoph Hellwig 2017-10-06 17:41 ` Nicolas Pitre 2017-10-06 17:41 ` Nicolas Pitre 2017-10-06 2:45 ` [PATCH v5 5/5] cramfs: rehabilitate it Nicolas Pitre 2017-10-06 2:45 ` Nicolas Pitre 2017-10-06 6:39 ` [PATCH v5 0/5] cramfs refresh for embedded usage Christoph Hellwig 2017-10-06 6:39 ` Christoph Hellwig 2017-10-06 16:07 ` Chris Brandt 2017-10-06 16:07 ` Chris Brandt 2017-10-06 16:30 ` Nicolas Pitre 2017-10-06 16:30 ` Nicolas Pitre
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